m 



THEi 

rR,EArrME^]siT 



CRUCIBLE STEEL 

COMPANY OF 

AMERICA 



Ct, ^* ^ 



The Treatment of Steel 



The Treatment of Steel 

A Compilation from Publications of 
the Crescent Steel Company on 

Heating, Annealing, Forging, Hardening and Tempering 

and on the use of Furnaces ; also a chapter on 

Hardening and Tempering from a work 

by .George Ede, Woolwich 

Ars.enal, England 




Crucible Steel Company of America 

Pittsburgh, Pennsylvania, U. S. A. 
1902 






Copyright, iSSi, by Miller, MetcaU'& Parkin 

Reprint by Crescent Steel Company 

Revised and reprinted, 1902, by Crucible Steel Company ot America 



4S6666 
W- 4, '35 



X^ 



^ 



Bartlett iK; Company 

The Orr Press 

New York 



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ri 



O 

r^ Preface to the Third Edition 



3" 



"Steel," as Arnold well expresses it, "is a marvelously 
complex material, containing always more or less of the 
following elements in addition to iron : carbon, silicon, 
manganese, sulphur and phosphorus. Besides these con- 
stituents, there may be present by design or accident the 
following : — tungsten, chromium, aluminium, nickel, copper, 
arsenic," . . . and, we may add, molybdenum. 

" In addition to these elements, steel contains the gaseous 
bodies, hydrogen and nitrogen, and sometimes oxygen." 

Altogether, as Dr. Dudley points out, there are " fifteen 
or twenty elements occurring in and affecting the quality 
of iron and steel," while Carnot and Goutal call attention 
to the fact that through purely chemical methods four 
conditions of carbon have been detected : — "graphite or free 
crystallized carbon ; graphitic carbon or temper carbon ; 
the carbon of the carbide of iron (cement carbon) and 
hardening carbon." 

The microscope reveals four constituents in carbon 
steel : — " ferrite or nearly pure malleable iron ; sorbite or iron 
slightly carburetted ; pearlite, composed of alternate plates 
of ferrite or sorbite and of the carbide Fe,C., and cemen- 
tite or the carbide Fe,C.," while, forming the bulk of 
hardened steel, " are three other constituents, martensite, 
troostite and austensite." 

" Of all the elements connected with steel," Arnold says, 
" carbon is by far the most important : as the blood is the 
life, so is the carbon the steel" — truly a wondrous metal, 
steel. 



Ridsdale, in the Journal of the British Iron and Steel 
Institute, tabulates twenty-four faults, under seven different 
types, observed by him in steel, and in tracing the probable 
causes he charges seven of these to the maker, nine to the 
user, and one to both. 

Treatment, therefore, and particularly heat treatment, is 
closely related to the behavior and value of steel. This 
third edition of " The Treatment of Steel " is issued at the 
request of many with the hope that it will be accepted as an 
effort to assist in overcoming difficulties connected with the 
working of a metal so complex ; if some find in it nothing 
that is new, others may be able to select something that will 
be of interest and profit. 



Crucible Steel Company of America 
A. L. B. 



July, 1902 




RKFINED ]',\ Ii.\Ki.)p:NING 




NATURAL 15AR 



The Treatment of Steel 

Annealing Steel 



Owing to the fact that the operations of rolling or 
hammering steel make it very hard, it is frequently necessary 
that steel should be annealed before it can be conveniently 
cut into required shapes for tools. 

Annealing or softening is accomplished by heating steel 
to a red heat and then cooling it very slowly, to prevent it 
from getting hard again. 

The higher the degree of heat the more the steel will 
be softened, until the limit of softening is reached when the 
steel is melted. 

It does not follow that the higher a piece of steel is 
heated the softer it will be when cooled, no matter how 
slowly it may be cooled ; this is proved by the fact that an 
ingot is always harder than a rolled or hammered bar made 
from it. 

Therefore, there is noth- 
ing gained by heating a 
piece of steel hotter than 
a good bright cherry red ; 
on the contrary, a higher 
heat has several disadvan- 
tages : 

First — If carried too 
far, it may leave the steel 
actually harder than a good 
red heat would leave it. 




8 The Treatment of Steel 

Second — If a scale is raised on the steel, this scale will 
be harsh, granular oxide of iron, and will spoil the tools used 
to cut it. It often occurs that steel is scaled in this way, 
and then because it does not cut well, it is customary to 
heat it again, and hotter still, to overcome the trouble ; 
while the fact is, that the more this operation is repeated, 
the harder the steel will work, because of the hard scale and 
the harsh grain underneath. 

Third — A high scaling heat, continued for a little time, 
changes the structure of the steel, destroys its crystalline 
property, makes it brittle, liable to crack in hardening, and 
impossible to refine.* 

Again, it is a common practice to put steel into a hot 
furnace at the close of a day's work, and leave it there all 
night. This method always gets the steel too hot, always 
raises a scale on it, and worse than either, it leaves it soak- 
ing in the fire too long; and this is more injurious to steel 
than any other operation to which it can be subjected. 

A good illustration of the destruction of crystalline 
structure by long-continued heating may be had by operating 
on chilled cast-iron. 

If a chill be heated red hot and removed from the fire as 
soon as it is hot, it will, when cold, retain its peculiar crystal- 
line structure ; if now it be heated red hot, and left at a 
moderate rtd for several hours ; in short, if it be treated as 
steel often is, and be left in a furnace over night, it will be 

• 
*" In high-carbon tool steels a prolonged high heat may also throw 
the carbon out of its proper combination with the iron, giving a coarse 
grayish or blackish fracture. Such a steel will harden, but can never 
have the strength of one properly treated. It will break with a straight, 
' dead ' fracture and be lacking in toughness." — E. L. French. 



Annealing Steel 9 

found, when cold, to have a perfect amorphous structure, 
every trace of chill crystals will be gone, and the whole 
piece will be non-crystalline gray cast-iron. If this is the 
effect upon coarse cast-iron, what better is to be expected 
from fine cast-steel ? 

A piece of fine tap steel after having been in a furnace 
over night will act as follows : 

It will be harsh in the lathe and spoil the cutting tools. 

When hardened it will almost certainly crack ; if it does 
not crack it will have been a remarkably good steel to begin 
with. When the temper is drawn to the proper color and 
the tap is put into use, the teeth will either crumble off or 
crush down like so much lead. 

Upon breaking the tap the grain will be coarse and the 
steel brittle. 

To anneal any piece of steel, heat it red hot ; heat it 
uniforjiily and heat it tkroiig/i, taking care not to let the ends 
and corners get too hot. 

As soon as it is hot take it out of the fire, the sooner the 
better, and cool it as slowly as possible. A good rule for 
heating is to heat it at so low a red that when the piece is 
cold it will still show the blue gloss of the oxide that was 
put there by the hammer or the rolls. 

Steel annealed in this way will cut very soft ; it will 
harden very hard, without cracking, and when tempered it 
will be very strong, nicely refined and will hold a keen, 
strong edge. 



Heating Steel 



Owing to varying instructions on a great many different 
labels, we find at times a good deal of misapprehension as 
to the best way to heat steel ; in some cases this causes too 
much work for the smith, and in other instances disasters 
follow the act of hardening. 

There are three distinct stages, or times of heating : 

First — For forging. 

Second— For hardening. 

Third — For tempering. 

The first requisite for a good heat for forging is a clean 
fire and plenty of fuel, so that jets of hot air will not strike 
the corners of the piece; next, the fire should be regular, 
and give a good uniform heat to the whole part to be forged. 
It should be keen enough to heat the piece as rapidly as 
may be, and allow it to be 
thoroughly heated through, 
without being so fierce as to 
overheat the corners. 

The trouble in the forge 
fire is usually uneven heat, 
and not too high heat. Sup- 
pose the piece to be forged 
has been put into a very hot 
fire, and forced as quickly as 
possible to a high yellow 
heat, so that it is almost up 
to the scintillating point. If 
this be done, in a few minutes 




Heating Steel 1 1 

the outside will be quite soft and in nice condition for forging, 
while the middle parts will be not more than red hot. The 
highly heated soft outside will have very little tenacity ; that is 
to say, this part will be so far advanced toward fusion that the 
particles will slide easily over one another, while the less highly 
heated inside parts will be hard, possessed of high tenacity, 
and the particles will not slide so easily over each other. 

Now let the piece be placed under the hammer and 
forged, and the result will be as shown in Fig. i. 

The soft outside will yield so much more readily than 
the hard inside, that the outer particles will be torn asunder, 
while the inside will remain sound, and the piece will be 
pitched out and branded "burned." 




Fig. 2 

Suppose the case to be reversed and the inside to be 
much hotter than the outside ; that is, that the inside shall be 
in a state of semi-fusion, while the outside is hard and firm. 

Now let the piece be forged and we shall have the case 
as shown in Fig. 2. The outside will be all sound and the 
whole piece will appear perfectly good until it is cropped, 
and then it is found to be hollow inside, and it is pitched 
out and branded '- burst." 

In either case, if the piece had been heated soft all 
through, or if it had been only red hot all through, it could 
have been forged perfectly sound and good. 



12 The Treatment of Steel 

If it be asked, why then is there ever any necessity for 
smiths to use a low heat in forging, when a uniform high 
heat will do as well, we answer: 

In some cases a high heat is more desirable to save 
heavy labor, but in every case where a fine steel is to be 
used for cutting purposes, it must be borne in mind that very 
heavy forging refines the bars as they slowdy cool ; and if the 
smith heats such refined bars until they are soft, he raises 
the grain, makes them coarse, and he cannot get them fine 
again unless he has a very heavy steam hammer at command 
and knows how to use it well. 

In following the above hints there is a still greater 
danger to be avoided : that is incurred by letting the steel 
lie in the fire after it is properly heated. When the steel is 
hot through it should be taken from the fire immediately 
and forged as quickly as possible. 

" Soaking" in the fire causes steel to become *' dry " and 
brittle, and does it more injury than any bad practice known 
to the most experienced. 

By observing these precautions a piece of steel may 
always be heated safely, up to even a bright yellow heat, 
when there is much forging to be done on it ; and at this 
heat it will weld well. 

The best and most economical of welding fluxes is clean, 
crude borax, which should be first thoroughly melted and then 
ground to fine powder. Borax prepared in this way will not 
froth on the steel, and one-half of the usual quantity will do 
the work as well as the whole quantity unmelted. 

After the steel is properly heated it should be forged to 
shape as quickly as possible, and just as the red heat is 
leaving the parts intended for cutting edges these parts 



Heating Steel i -^ 

should be refined by rapid liglit blows, continued until the 
red disappears. 

For the second stage of heating for hardening great care 
should be used, first, to protect the cutting edges and work- 
ing parts from heating more rapidly than the body of the 
piece; next, that the whole part to be hardened be heated 
uniformly through, without any part becoming visibly hotter 
than the other. A unif(3rm heat, as low as will give the 
required hardness, is the best for hardening. 

Bear in mind, that for every variation of heat which 
is great enough to be seen there will result a variation in 
ORAiN, which may be seen by breaking the piece, and for 
every such variation in temperature there is a very good 
chance for a crack to be seen. Many a costly tool is ruined 
by inattention to this point. 

The effect of too high heat is to open the grain, to 
make the steel coarse. 

The effect of an irre(;ular heat is to cause irregular 
grain, irregular strains, and cracks. 

As soon as the piece is properly heated for hardening it 
should be promptly and thoroughly quenched in plenty of 
the cooling medium, water, brine or oil, as the case may be. 

An abundance of the cooling bath, to do the work 
quickly and uniformly all over, is very necessary to good 
and safe work. 

To harden a large piece safely a running stream should 
be used. 

Much uneven hardening is caused by the use of too small 
baths. 

For the third stage of heating ; to temper, the first im- 
portant requisite is again uniformity. The next is time ; 



14 



The Treatment of Steel 



the more slowly a piece is brought down to its temper, the 
better and safer is the operation. 

When expensive tools, such as taps, rose cutters, etc., are 
to be made, it is a wise precaution, and one easily taken, to 
try small pieces of the steel at different temperatures, so as 
to find out how low a heat will give the necessary hardness. 
The lowest heat is the best for any steel, the test costs 
nothing, takes very little time, and very often saves consider- 
able losses. 




Furnaces 



On the following pages we present sketches of a cheap 
and handy furnace for use in a blacksmith shop, adapted 
especially for heating steel, and more particularly for heat- 
ing steel for hardening. 

The furnace is so simple that the sketches need no 
explanation ; for binders, ten pieces of old rail about six 
feet long with one end set in the ground and the tops tied 
by ^-inch rods are all that is necessary, with a piece of 
iron about 3 x ^ inch running around near the top, and 
set in flush with the bricks. 

The distinctive features of this furnace are the fire bed 
and a good damper on the stack. In an experience of many 
years we have found nothing better than the Tupper grate- 
bar with i^-inch openings. These bars set in as shown 
make a level, permanent bed, and give an evenly distributed 
supply of air to the fuel. In such a furnace as this one set 
of bars will last for years and remain level. 








1 6 The Treatment of Steel 

While on the subject of grate-bars we may as well say 
that the satisfactory and safe working of this furnace would 
be entirely defeated by any attempt to use either square 



[2 9 6 3 o 




LuJiiJjdJiji 



Scale: 4^=1 foot. 

ID 

Stack 15 to 20 high 



wrought-iron bars or ordinary straight cast-iron bars. Such 
bars always warp, get pushed out of place, and allow a rush 
of air through at one place and no air at another. This 
causes hot and cold places in the furnace and produces 



Furnaces 



T7 



uneven heating, which is the chief source of cracking in 
hardening, and also the air rushing through the large holes 
will burn the steel. A bar must be used which will remain 
level and in its place, and the smaller and more numerous 
the openings are the better will be the result. 

Clean, hard coke is the only proper fuel for such a furnace 
and for such work. The furnace should be filled full up to 



SECTION A E 



[3 in. _ ,4*, 
luare'l ~ i 




the fore plate — or better, a little higher — with coke in pieces no 
larger than an ordinary man's fist, but the smaller the better. 

When it is used for heating for forging purposes the 
damper may be left high enough to run the furnace as hot as 
may be required — if necessary, a welding heat can be obtained. 

When used for hardening, the furnace should be got 
as hot as is needed before the steel is put into it — then 



The Treatment of Steel 



when the steel is put in, the damper should be dropped 
down tight. 

The door, which is 12 inches high and 24 inches 
wide, should be nicely balanced by a lever and weight, 
with a rod in a handy place so that the operator can 
pull it up easily and turn over his pieces from time to 
time, so as to get his heat perfectly uniform. 

In the clear gas of a coke fire the whole interior of 
a furnace can be seen easily, and every piece can be watched 

as it ought to be. Time, 
care, watchfulness and 
absolute uniformity of 
heat are the essentials 
necessary for success in 
hardening steel. 

Every large shop 
should have such a 
furnace, and should 
have one man trained 
to its use, to do the 
hardening and temper- 
ing for the whole shop. 
Such a furnace in the hands of a careful man in any rail- 
road shop in the country would pay for itself every year 
and save the man's wages besides. 

The furnace will consume very little coke at any time, 
and when not in use, with the damper down, it will stay hot 
a long time and waste the coke but a trifle. 

There is no more absurd nor wasteful system than 
that of requiring a smith at his anvil to harden and 
temper his work. His fire is not fit to heat in, to 




Furnaces t 9 

begin with, and he never has time to do his work properly, 
if it were. 

From such a furnace as is here described we harden all 
sorts of tools, taps, small dies, large rolls, rotary shear 
knives, and shear knives as large as five feet long, which is 
the whole length of the furnace. 

The steel which is hardened and tempered best is the 
finest in the grain and the strongest. The best way to test 
both grain and strength is to hammer out a piece to about 
i}( X ji inch, a foot or so in length, harden it at a heat 
which is considered nearly right for the particular piece, and 
temper to a high blue, or pigeon wing, and when cold to 
break it ofT in little pieces with a hand hammer. A little 
practice will soon enable a man to determine if he heated 
the piece to just the right point in hardening. A fine, silky 
grain will show this, and the hammer and file, respectively, 
will tell whether the tempering has made the stock tough 
enough and of the proper degree of hardness for the work 
the steel must do. 

In every shop there are plenty of worn-out tools of all 
sorts in the scrap heap ; the temperei should be allowed to 
spend all of his leisure time in hammering these out and 
testing them as above. The steel will cost nothing, and the 
knowledge gained will pay for the time over and over again. 
We say to our friends again that if you will heat even the 
finest steel in dirty slack fires you will get dirty coats of 
sulphurous oxides on it, and no good results. 

The cost of such a furnace as we have described is about 
one hundred and fifty dollars. 



Effects of Heat Upon Steel 

We give herewith a description of the method by which 
any worker in steel should be able to obtain a satisfactory 
illustration of the effect of heat upon steel. 

Description — Take a bar of steel of ordinary size, say 
about I inch by )4, and heat 6 or 8 inches of one end to a 
low red heat, and nick the heated part all around the bar at 
intervals oi }4 to % of an inch, until eight or nine notches 
are cut. Next place the end of the bar in a very hot fire 
and heat it white hot until it scintillates at the extreme 
end, leaving the other parts enough out of the fire to heat 
them only by conduction. Let the end remain in the fire 
until the last piece nicked is not quite red hot, and the 
next to the last barely red hot. 

Now, if the pieces be numbered from i to 8, commencing 
at the outer end, No. i will be white or scintillating hot. 
No. 2 will be white hot. No. 3 will be high yellow hot. No. 4 
will be yellow or orange hot. No. 5 will be high red hot, No. 

6 wdll be red hot. No. 7 will be low 
red hot, No. 8 will be black hot. 

As soon as heated, let the bar 
be quenched in cold w^ater and 
kept there until quite cold. After 
cooling, the bar should be care- 
fully wiped dry, especially in the 
notches. An examination by the 
file will reveal the following, if 
high steel has been used : 

No. I will scratch glass, Nos. 
2, 3 and 4 excessively hard, Nos. 




Crucible Steel Company of America 




Effects of Heat upon Steel 



Effects of Heat Upon Steel 21 

5 and 6 well hardened, No. 7 about hard enough for tap 
steel, No. 8 not hardened. 

Now break off the pieces over the corner of the anvil. 
They should be caught in a clean keg or box, to keep the 
fractures clean and bright. 

No. I will be as brittle as glass, No. 2 will be nearly as 
brittle as glass, Nos. 3, 4 and 5 will break off easily, each a 
little stronger than the other, Nos. 6 and 7 will be very strong, 
and much stronger than No. 8, or the bar unhardened. 

Place the pieces in the order of their numbers fitting the 
fractures, then up-end each one, beginning with No. i and 
following with each in the order in which they lie, and the 
result will be fractures which any ordinary skilled eye can 
appreciate, each differing from the other. 

No. I will be coarse, yellowish cast, and very lustrous ; 
No. 2 will be coarse and not quite so yellow as No. i : No. 3 
will be finer than i or 2, and coarser than No. 8, and will 
iiave fiery luster ; No. 4, like No. 3, not quite so coarse, yet 
coarser than No. 8 ; No. 5 will be about the same size grain 
as No. 8, but will have fiery luster ; No. 6 will be much finer 
than No. 8, will have no fiery luster, will be hard nearly 
through and very strong. This is what is called refining by 
hardening. No. 7 will be refined and hard on the corners 
and edges, and coarser and not hard in the middle. This 
is about the right heat for hardening taps, milling tools, 
etc., the teeth of which will be amply hard, while there will 
be no danger of cracking the tool.* No. 8 illustrates the 
original grain of the bar. 

* Note by A. L. B. — On the other hand it is contended by one of 
our writers that the temperature indicated by No. 6 is right for all 



22 The Treatment of Steel 

In nine cases out of ten the bar will crack along the 
middle to the refined piece. In tests made we have had 
the crack show plainly, but we have never known this 
crack to extend into the refined piece, although we have 
repeated the experiment many times. We learn from this 
experiment the following : 

First — (^) Any difference in temperature sufficiently 
great to be seen by the color will cause a corresponding 



hardened work, including taps, reamers and milling cutters, and that a 
superficial hardening, such as is shown in No. 7, is fatal to the class of 
tools mentioned, because they are almost certain to crack in the hard- 
ening process. It must be borne in mind, however, that the hardening 
is effected upon flat surfaces in the series of fractures shown, whereas, 
in the case of toothed tools, the small projections are acted upon by 
the chilling medium and are hardened through, while the hardening 
also extends into the body of the tool. It is true that No. 6 is the 
ideal condition for all hardened steel, wherever that condition can be 
attained, but the degree of heat that, in a tap of considerable size, would 
carry the hardening through to the center, would overheat the project- 
ing teeth unless very carefully applied. And such overheat would 
mean an exchange of the structure of No. 7 for a combination of the 
coarser grain of No. 5 (in the projections) with the refined structure of 
No. 6 (in the body), a variation in grain which would result in cracking 
and crumbling. 

A beautiful exemplification of superficial hardening as shown in 
No. 7, is that of long stay-bolt taps when heated for hardening in iron 
pipes in which the tool is kept turning while the heat is being applied 
through the walls of the pipe. A tap so treated is soft enough in the 
center to be drilled, while the teeth are well hardened and refined. 

The statement in tlie text may, perhaps, be made clearer if we add : 
Heat the tool evenly through without letting the cutting parts get 
hotter than the refining heat, shown by No. 6, and these parts will be 
well hardened while the body of the tool will be hard enough. 



Effects of Heat Upon Steel 23 

difference in the grain, {b) This variation in grain will 
produce internal strains and cracks. 

Second— Any temperature so high as to open the grain 
so that the hardened piece will be coarser than the original 
bar will cause the hardened piece to be brittle, liable to 
crack, and to crumble on the edges in use. 

Third— A temperature high enough to cause a piece 
to harden through, but not high enough to open the 
grain, will cause the piece to refne, to be stronger than 
the untempered bar, and to carry a tough, keen, cutting 
edge. 

Fourth — A temperature which will harden and refine 
the corners and edges of a bar, but which will not harden 
the bar through, is just the right heat at which to harden 
taps, rose-bitts and complicated cutters of any shape, as it 
will harden the teeth sufficiently without risk of cracking, 
and will leave the mass of the tool soft and tough, so that it 
can yield a little to pressure and prevent the teeth tearing 
out.* These four rules are general, and apply equally well 
to any quality of steel or to any temper of steel. 

Steel which is so mild that it will not harden in the ordi- 
nary acceptance of the term will show differences of grain 
corresponding to variations in temperature. 

To restore any of the first seven pieces shown to the 
original structuref as shown in No. 8, it is only necessary to 
heat it through to a good red heat, not to a high red, allow 

* See foot note page 21. 

t Note by A. L. B. — The author means physical structure. As to 
his opinion of the value of at least two of the pieces, say, Nos. i and 
2, when so restored, see his final paragraph on next page. Also com- 
pare page 50. 



24 The Treatment of Steel 

it to stay at this temperature for ten minutes to thirty minutes, 
according to the size of the piece, and then to cool slowly. 
If upon the first trial the restoration should be found incom- 
plete, and the piece upon being fractured should still show 
some fiery grains, a second heating continued a little longer 
than the first would cause a restoration of fracture. This 
property of restoration is not peculiar to any steel, and its 
performance requires no mysterious agencies beyond those 
given above. 

It should be distinctly borne in mind that a piece restored 
from overheating is never as good as it would have re- 
mained if it had not been abused, and we strongly advise 
that no occasion should ever be given for the use of this 
process of restoration except as an interesting experiment. 
The original and proper strength of fine steel can never be 
FULLv RESTORED after it has once been destroyed by over- 
heating. 



On Temper of Steel 



The word temper, as used by the steel maker, indicates 
the amount of carbon in steel ; thus, steel of high temper is 
steel containing much carbon ; steel of low temper is steel 
containing little carbon ; steel of medium temper is steel 
containing carbon between these limits, etc. Each number 
of our carbon circular represents a temper, and besides 
these numbers we use intermediate ones, amounting to some 
twenty in all. As the temper of steel can only be observed 

in the ingot, it is not neces- 
sary to the needs of the trade 
to attempt any description of 
the mode of observation, es- 
pecially as this is purely a 
matter of education of the 
eye, only to be obtained by 
years of experience. 

The act of temperuig steel 
is the act of giving to a piece 
of steel, after it has been 
shaped, the hardness neces- 
sary for the work it has to do. This is done by first 
hardening the piece, generally a good deal harder than is 
necessary, and then toughening it by slow heating and 
gradual softening until it is just right for work. 

A piece of steel properly tempered should always be finer 
in grain than the bar from which it was made. If it is 
necessary, in order to make the piece as hard as is re- 
quired, to heat it so hot that after being hardened it will be 




26 The Treatment of Steel 

as coarse or coarser in grain than the bar, then the steel 
itself is of too low temper for the desired work. In a case 
of this kind the steel maker should at once be notified of 
the fact, who should immediately correct the trouble by 
furnishing higher steel. 

If a great degree of hardness is not desired, as in the 
case of taps, and most tools of complicated form, and it is 
found that at a moderate heat the tools are too hard and are 
liable to crack, the smith should first use a lower heat in 
order to save the tools already made, and then notify the 
steel maker that his steel was too high, so as to prevent a 
recurrence of the trouble. In all cases where steel is used 
in large quantities for the same purpose, as in the making of 
axes, springs, forks, etc., there is very little difficulty about tem- 
per, because, after one or two trials, the steel maker learns 
what his customer requires, and can always furnish it to him. 

In large, general works, however, such as rolling-mills, 
nail factories, large machine works, or large railroad shops, 
both the maker and worker of the steel labor under great 
disadvantages from want of a mutual understanding. 

The steel maker receives his order and fills it with 
tempers best adapted to general work, and the smith usually 
tries to harden all tools at about the same heat. The steel 
maker is right, because he is afraid to make the steel too 
high or too low, for fear it will not suit, and so he gives an 
average adapted to the size of the bar. 

The smith is right, because he is generally the most hur- 
ried and crowded man about the establishment. He must 
forge a tap for this man, a cold nail knife for that one, and a 
lathe tool for another, and so on ; and each man is in 
a hurry. 



On Temper of Steel 27 

Under these circumstances he cannot be expected to stop 
and test every piece of steel he uses, and find out exactly at 
what heat it will harden best, and refine properly. 

He needs steel that will all harden properly at the same 
heat, and this he usually gets from the general practice 
among steel makers of making each bar of a certain temper, 
according to its size. 

But if it should happen that he were caught with only 
one bar of, say, inch-and-a-quarter octagon, and three men 
should come in a hurry, one for a tap, another for a punch, 
and another for a chilled roll plug, he would find it very 
difticult to make one bar of steel answer for all of these pur- 
poses, even if it were of the very best quality, and the chances 
are that he would make one good tool and two bad tools. 

There is a perfectly easy and simple way to avoid all of 
this trouble ; and that is, to write after each size the purpose 
for which it is wanted, as for instance: Track tools, smith 
tools, lathe tools, taps, dies, cold nail knives, cold nail dies, 
hot nails, hot or cold punches, shear knives, etc. This gives 
very little trouble in making the order, and it is the greatest 
relief to the steel maker. It is his delight to get hold of such 
an order, for he knows that when it is filled he will hardly 
ever hear a complaint. 

Every steel maker worthy of the name knows exactly 
what temper to provide for any tool, or if it is a new case, 
one or two trials are enough to inform him, and as he always 
has all of his twenty odd tempers on hand, it is just as easy 
— and far more satisfactory to both parties — to have it made 
right as to have it made wrong. 

A Sheffield manufacturer calls attention to this same 
experience, and very truthfully remarks : 



2 8 The Treatment of Steel 

" For many purposes, indeed, temper is of more importance 
than quality. Nothing is more common than for steel to be re- 
jected as bad in quality, because it has been used for a purpose 
for which the temper was unsuitable. We may divide con- 
sumers of steel into three classes : First, those who use their 
own judgment of what percentage of carbon they require, and 
instruct the manufacturer to send them steel of a specified 
temper ; second, those who leave the selection of the temper 
to the judgment of the manufacturer, and instruct him to send 
them steel for a specified purpose ; and third, those who 
simply order steel of a specified size, leaving the manufacturer 
to guess for what purpose it is required. It cannot too 
often be reiterated of how much importance it is, when 
ordering steel, to state the purpose for which it is going to 
be used." 

And again : 

"You may depend upon it there is nothing so dear as 
cheap steel. It must be more economical to put five shil- 
lings' worth of labor upon steel that costs a shilling, to pro- 
duce a tool that lasts a day, than to put the same value of 
labor upon steel that costs only ninepence, to produce a 
tool that lasts only half a day. I am sure that the system 
adopted by some large consumers of buying tool steel by 
tender is one which in too many cases defeats the object for 
which it was instituted, and, by lessening the price, and con- 
sequently deteriorating the quality, causes the steel bill to be 
lessened at the cost of the labor bill, so that extravagance 
instead of economy is the result. In fact, it is an illus- 
tration of the proverb about being penny wise and pound 
foolish." 



On Gauges 



In consequence of the absurdities and anomalies existing 
in our present system of gauges, we recommend the use of 
the inch as a unit of measurement. 

There are in use at the present time three standard gauges. 

It may be possible to make one gauge to any of these 
standards which shall be so accurate as to defy the detection 
of an error, and with the same care it may be possible to 
make a thousand such gauges ; but every mechanic, and 
every person accustomed to making accurate measurements 
of the best work, knows that it is simply impossible to 
obtain absolute accuracy in such pieces of work when 
produced in large quantities, and it is impossible covwiercially^ 
on account of the cost. 

We therefore recommend the use of the micrometer sheet 
metal gauge, which measures thousandths of an inch very 
accurately, and a skilled mechanic can determine even a 
quarter of a thousandth with precision. 




Why Does Steel Harden ? 



By W. Metcalf, C. E. 



The inquiry has been pursued diUgently by Prof. John 
W, Langley and ourselves for the past five years, and has 
been directed exckisively to the gathering of facts, so that 
as yet we have not even a theory to offer. The inquiry 
may be divided as follows : 

1. The physical structure of steel. 

2. The chemical composition. 

3. The variations of structure and physical properties 
due to — 

a. — Cooling from fusion. 

b. — Effect of work, either by rolling or hammering. 
c. — Effect of temperature, and of changes from one tem- 
l)erature to another, as shown by slow cooling or rapid cooling. 

4. A statement of the various theories of hardening. 

5. Some practical conclu- 
sions for workers of steel. 

1. The physical structure 
of steel. 

In this paper it is to be 
understood that reference is 
made only to cast-steel. 

Steel is crystalline in struc- 
ture. The size, color and form 
of the crystals, when steel is 
allowed to cool without hind- 
rance from a state of fusion, 
are governed by its chemical 




IVby Does Steel Harden ? 3 i 

constitution, and are mainly influenced by the quantity of 
carbon present. 

2. The chemical composition of steel. 

Steel is mainly an alloy, compound or mixture of iron 
and carbon. 

Exactly which of these it may be, or whether it is a com- 
bination of two or of all three of these conditions, it is 
difficult to say. 

Other elements,as silicon, phosphorus,sulphur, manganese, 
and so on, are as yet present only by sufferance, and gene- 
rally it is well known that steel is better without any of them. 

The range of carbon in commercial steel may be said to 
be from about .05 per cent, to 1.75 or 2 per cent., but for 
some purposes of this inquiry we may look at several proper- 
ties of cast-iron as being useful to throw light on the subject. 

3. The variations of structure and physical properties 
due to- 
rt;. — Cooling from fusion — as afl^ected by chemical com- 
position, temperature, and rate of cooling. 

The structure of steel, and of cast-iron, as shown- in a 
fresh fracture of the ingot in one case, or the pig in the 
other, is remarkable as always indicating the quantity of 
carbon present, the temperature at which the metal was 
poured, and the rate of cooling. 

As the observation of these phenomena furnishes material 
for the study of a lifetime, and as they cannot be described 
properly without the objects themselves, only a few well- 
known facts will be mentioned, for use in the latter part of 
this paper. Cast-iron, when poured into iron moulds, hardens 
just as steel does when quenched in water ; this is known as 
" chilling." 



-^2 The Treatment of Steei 

x\ chill is of silvery white color, bright luster and consists 
of elongated crystals generally normal lengthwise to the sur- 
face of the mould. 

If iron contains little or no silicon, it will chill very deep, 
or entirely through the mass in small castings. 

If much silicon be present it will not chill at all. 

If a hard chill — for instance in a hammer die — say two 
inches thick of chill, be brought to a red heat, removed from 
the fire at once and allowed to cool slowly, it will, when 
broken, be found to be softened, but it will retain the marked 
crystalline form of the chill. This is analogous to tempered 
steel. 

If the same chill be heated red, and kept red hot for sev- 
eral hours, and then cooled slowly, it will be found upon break- 
ing to be an entirely amorphous gray cast-iron ; every trace 
of the elongated crystals of the chill will have disappeared. 

This is analogous to annealed steel. This experiment is 
a striking example of iron and combined carbon in the one 
case, and of iron and graphitic carbon in the other case, as 
these conditions are commonly understood. 

This observation is useful in understanding similar 
changes which occur in steel under the similar conditions of 
hardened, tempered and annealed steel. 

Steel when cast is almost invariably poured into iron 
moulds, and the study of fractured ingots is very necessary 
to the steel maker ; but as the ingots very rarely go into the 
hands of the consumer without previous manipulation, it is 
hardly necessary to consume time in discussing the charac- 
ters of the fractures, especially as it requires the actual 
presence of the ingots to make the description at all 
intelligent. 



IVby Does Steel Harden ? 33 

It is sufficient to say that we have here an unvarying 
record of the completeness or incompleteness of the fusion, 
of the rate and temperature of the pouring, and of the 
chemical character of the steel, especially as it relates to 
carbon. 

b. — Effect of work, either by hammering or rolling. 

Steel, when heated and hammered or rolled from the 
ingot, has its specific gravity largely increased, its strength 
is greatly increased, and its grain is made v6ry fine and uni- 
form ; this is called " hammer refining," to distinguish it 
from the refining due to hardening. 

An eminent Russian engineer has illustrated this hammer 
refining beautifully by comparing the hot steel to a certain 
solution of a salt. 

If the solution be allowed to precipitate slowly and undis- 
turbed, very large crystals will be formed, but if it be vio- 
lently shaken, the crystallization is hastened and very fine 
crystals are formed. 

So if steel be heated quite hot, but not so as to burn 
it, and be allowed to cool very slowly, it will form in very 
large, bright crystals and be very friable ; but if as 
soon as it is hot it be taken to a heavy hammer and 
be thoroughly hammered by rapid and powerful blows 
at first, and then by lighter blows until it is of the re- 
quired shape, it will be found to be very fine in grain 
and very strong. 

Therefore, a high softening heat is consistent with good 
work in forging. 

c. — Effects of temperature, and of changes from one tem- 
perature to another, as shown by slow cooling or rapid 
cooling. 



34 The Treatment of Steel 

The effect of heating steel which has been hammered or 
rolled is to increase the size of the crystals or grain, in pro- 
portion to the temperature, and to reduce the specific gravity. 
There is an apparent or real exception to this increase in 
size of grain in steel which has been hardened from the proper 
temperature to produce what is known as "refining." 

In this case the grain is much finer than in the bar, and 
in this condition any piece of hardened and tempered steel 
is at its best. 

As this refining temperature varies with every different 
quantity of carbon, no rule can be laid down for determining 
it ; it must be found by actual trial. 

But there is no exception to the matter of specific grav- 
ity. The specific gravity of refined steel is less than that of 
the bar, although the grain is much finer. If steel be heated 
and cooled slowly it will be softened ; that is, annealed. 

If it be heated very hot, say to bright yellow, or kept hot 
a long time, and then cooled slowly, it will still be annealed, 
but it will be harsh and gritty, will not cut well, and will 
neither refine well when hardened nor hold a good edge 
when tempered. The cause of this will be obvious if we re- 
member the experiment of the annealed chill mentioned in 
the earlier part of this paper. If steel be heated to different 
degrees, as red, bright red, orange, lemon or bright yellow 
color, and quenched, it will be found to be harder, more 
brittle, and coarser in the grain for each increasing degree of 
heat, after the "refining" heat has been passed. Below the 
"refining" heat there will be no useful degree of hardening, 
and the grain will be variable. 

If any piece of hardened steel be heated red hot, and 
cooled slowly, it will be softened, the grain of the steel 



IVby Does Steel Harden ? 3 5 

will return to its original appearance in the bar, and its spe- 
cific gravity will be restored to the specific gravity of the bar. 

This fact should put a quietus upon all quack nostrums 
for " restoring burnt steel." 

If a piece of steel containing little carbon be alternately 
hardened and heated and re-hardened a number of times, it 
will vary in volume, but will not sustain regular increases of 
volume. 

- If steel of moderately high carbon be repeatedly hard- 
ened it will continue to increase in volume until ruptured. 
This will be illustrated by table No. 5. 

Some years ago twelve ingots were selected by numbers, 
and analyzed to determine the accuracy of ocular inspection, 
and were afterward experimented upon in following up the 
search for facts in regard to the cause of " hardening." 

The specific gravities of these ingots were determined, 
and the results were given by Prof. Langley in a paper read 
before the American Association for the Advancement of 
Science, in 1876. Since then, bars rolled from these ingots 
have been experimented upon, and the specific gravities of 
the bars and of various hardened pieces and of re-softened 
pieces have been determined. 

These experiments will now be described. 

Table I gives the analyses and specific gravities of the 
ingots. 

Table II gives the specific gravities of six of the bars, 
and the specific gravities of the same bars heated to various 
temperatures and hardened. 

Table III gives the specific gravities of the six bars, and 
the six hottest pieces numbered i in Table II, after having 
been annealed from the condition given in Table II. 



,16 



The Treatment of Steel 



Table IV gives the specific gravities of four pieces, all 
from the same bar, after various treatment. 

Table V gives the results of repeated hardening of 
three pieces of steel containing different quantities of 
carbon. 

Consideration of the tables : 

Table I contains the analysis of twelve ingots, numbered 
in the left-hand column from i to 12. 



Table I 



Ingot 


c. 


Si. 


Ph 


s 


Fe. by 


Sp. Gr. 


•Numbers 






Difference 


Ingots 


J 


.302 


.019 


•047 


.018 


99.614 


7.855 


2 


.490 


•c534 


.005 


.016 


99-455 


7.836 


3 


•529 


•043 


.047 


.018 


99363 


7.841 


4 


.649 


•039 


.030 


.012 


99.270 


7.829 


5 


.801 


.029 


•035 


.016 


99.119 


7.838 


6 


.841 


•039 


.024 


.010 


99.086 


7.824 


7 


.867 


.057 


.014 


.018 


99.044 


7.819 


8 


.87 1 


•053 


.024 


.012 


99.040 


7.81S 


9 


•955 


•059 


.070 


.016 


98 900 


7-813 


10 


i.oos 


.088 


■034 


.012 


98.861 


7.807 


\ I 


1058 


.120 


.064 


.006 


98.752 


7.803 


12 


1.079 


•039 


.044 


.044 


98.834 


7.805 



The ingots were selected by the eye and numbered as in 
the table by Mr. Charles Parkin, with a view to varying 
quantities of carbon only. 

It will be seen that the carbon increases with the num- 
bers regularly, but not uniformly. 

Although a repetition of the analyses of Nos. 7 and 8 
confirm Prof. Langley in the correctness of his figures, it 
must be admitted that in this case Mr. Parkin was quite as 



Why Does Steel Harden ? 



M 



lucky as skillful, for it is hard to believe in a really observa- 
ble variation of structure due to a difference of only 0.004 
carbon. 

In the columns for Si., Ph. and S. the entire absence of 
progressive quantities shows clearly that these elements had 
nothing to do in determining the characteristic fractures. 

The column of iron by difference happens to run with 
tjie carbon column, except in No. 11, where the series is 
broken by the abnormal amount of Si. in that ingot. Theo- 
retically, of course, the specific gravities should run with the 
iron by difference, but they do not do so in ingots 3 and 5. 
These, however, are the only exceptions ; this may have 
been caused by incomplete or unusually hot melting, or by 
hot or cold pouring, or by slow or fast pouring. 

These exceptions do not vitiate the rule, and only show 
that no one set of experiments can be conclusive. 

Table II 





to 


1. 


1 


^0 




u 


u 






«. 




1- 











i 






CO 




a. 

CO 


!« 

5* 


^1 








3 


7-841 


7.844 


.00^ 


7.8V 


-.0,, 


7.826 


-.018 


7-823 


-.021 


7.814 


-.030 


7.818 


-.026 


4 


7.«2q 


7.824 


-.005 


7.806 


-.0187.S49 


-.025 


7.830 


.006 


7. 811 


-.013 


7-791 


- 


033 


6 


7.824 


7.82q 


.cos 


7.812 


-.0177-808 


-.021 


7-780 


-.049 7.784 


-•035 


7.789 


- 


040 


8 


7.818 


7.82s 


.007 


7.790 


-•035,7-773 


-.042 


7-758 


-.067 7.75s 


-.070 


7-752 


- 


073 


10 


7.807 


7.826 


.019 


7.8.2 


-.oi4J7.7Sq 


--037 7-755 


-.071 7.749 


-.077 


7-744 


- 


OcS2 


12 


7.805 


7.825 


.020 


7. 811 


-.01^7-798 


-.0277-769 

1 


-.056 7.741 


-.084 


7.690 


--•35 




1 

6 


5 


4 


3 


2 


1 


Not 
heated 


Low red 
heat 


Red 
hot 


High 
red 


Yellow 
hot 


Nearly 
white Scin- 
tillating 



38 The Treatment of Steel 

The twelve ingots under consideration were hammered 
to lY^-moki square bars at one end, and these bars were 
rolled to .625 diameter round bars. 

Six of tnese bars, Nos. 3, 4, 6, 8, 10, 12, were selected 
for specific gravity tests ; bar No. 2 was lost, or it would 
have been used instead of No. 3. 

Six nicks were made around each bar at one end at 
intervals of about half an inch. 

The six pieces were numbered from i at the end to 6. 

Each notched bar was then heated until piece No. i was 
scintillating or nearly white hot ; No. 2 was yellow hot ; 
No. 3, high red hot; No. 4, red hot; No. 5, barely showing 
any red, or very low red hot ; No. 6, black. 

This heating was done in each case as slowly and as 
carefully as possible. The results show the inevitable 
irregularities attending only one such experiment, yet there 
is enough of regularity to teach us a great deal. 

As soon as the heats were obtained the bars were 
quenched in water. 

The pieces, carefully numbered, both with the ingot 
numbers and with the numbers giving their order on the 
bars, were then broken off and sent to Prof. Langley to have 
the specific gravities determined. In the table the left-hand 
column gives the ingot numbers. 

The other columns give the specific gravities of the ingots, 
the bars. No. 6 pieces, and of the other five hardened pieces 
in order, as numbered in the sketch and explained before. 

The differences are, first, the difference between the Sp. 
Gr. of the ingots and the bars ; second, the difference be- 
tween the Sp. Gr. of the bar, or piece No. 6, and each piece 
successively. 



IVby Does Steel Harden ? ;\ 9 

The differences of Sp. Gr. are given in preference to the 
actual differences in volume, because the differences in 
volume run into the infinitesimals, and the mode adopted 
answers as well for purposes of comparison. 

On comparing the ingot and bar we see a decided 
increase in the Sp. Gr. of the bar in every case except one, 
that of No. 4. We have not discovered the reason of this 
anomaly. The increase in the other cases is due to hot 
working; this will be shown by Table IV. 

It will be observed that the Sp. Gr. of the bars, except 
in No. 3, is nearly uniform. 

This seemed very strange at first, but it is capable of a 
very simple explanation. The hardness of steel and its 
resistance to change of form increase very rapidly with an 
increase of carbon, and as these bars were all reduced from 
3-inch square ingots to 5 g-inch round bars, it is obvious that 
it required much more work to reduce No. 12 than No. 4 
or No. 6 ; therefore, as hot working increases Sp. Gr., the 
greater amount of work produced the greater increase in the 
Sp. Gr. of No. 12. 

If the Sp. Gr. of the right-hand column pieces No. i be 
compared to the Sp. Gr. of the ingots, it will be seen that 
the relation between the numbers is entirely restored by the 
high heat to which the No. i pieces were subjected. 

If the Sp, Gr. of pieces Nos. 5, 4, 3 be examined care- 
fully, sufficient irregularities in the difference columns wdll 
be observed to show that the heating was not accomplished 
in regular gradations in each case, and if it were desired 
to lay down an exact law of variation due to differences of 
temperature, it would be necessary to take the mean of a 
great many experiments. 



40 The Treatment of Steel 

Nevertheless, several general laws are indicated in this 
table. 

1. The Sp. Gr. of the ingot varies directly with the 
quantity of iron present. 

2. The greater the quantity of carbon present, the 
greater is the amount of work necessary to produce change 
of form. 

3. The greater the quantity of carbon present, the 
greater is the change in volume due to a change of 
temperature. 

As, for example, in No. 3 the change in Sp. Gr. from the 
ingot to the bar in only .003, and from the same bar to the 
piece No. i the change is .026. 

While in No. 12 the change in Sp. Gr. from the ingot to 
the bar is .020, or about seven times that in No. 3, and the 
change from the bar to the piece No. i is .135, or about five 
times the change in No. 3. 

This is perhaps the most important observation that can 
be made on this series of experiments, as it shows us why it 
is that high steel is so much more liable to crack and break 
in manipulation than low steel. 

We generally say one is brittle and the other is ductile ; 
we now know that the rate of expansion per degree of 
temperature is much less in low steel than in high steel. 
Therefore, low steel is much less liable to injurious internal 
strains than high steel. 

In order to settle the question of restoring "burned 
steel," so called, and also to determine the reverse action 
due to annealing, Prof. Langley took the six pieces No. i of 
Table II, and heated them all to a high yellow heat. He 
then allowed them to cool very slowly. 



Why Does Steel Harden ? 



41 



This raised a heavy scale on the pieces, which was re- 
moved by touching them on an emery wheel. 

The specific gravities of these pieces were then taken, 
and the results are given in the table. 

The restoration to the Sp. Gr. of the bar is complete, as 
the differences are only such as might be due to the scale 





Tabl 


e III 




^T^"^U* 


Sp. Gr. of Bars 


Sp. Gr. of Burned 
Pieces 


Differences 


Numbers 


No. 5 


Annealed, No. i 




3 


7.844 


7.S57 


+ or3 


4 


7.824 


7.846 


+ .022 


6 


7.829 


7835 


+ .006 


8 


7.82s 


7.828 


+ .003 


10 


7.826 


7.824 


— .002 


12 


7825 


7.822 


-.003 



on the original bars and the removal of the scale from the 
annealed pieces. This will be shown further in Table IV. 

It is well known that cold rolling does not increase the 
Sp. Gr. of iron or of steel. To ascertain the effect of cold 
hammering under the best conditions to increase Sp. Gr., 
namely, by hammering between semi-circular dies, an experi- 
ment was made, the results of which are recorded in Table IV. 

A round bar, of carbon about i per cent., was operated 
upon. 

The bar, as it came from the rolls, and unannealed, was 
0.682 inch in diameter; this is No. i in the table. 

A piece of the same bar, annealed and pickled, was 0.673 
inch in diameter; this is No. 2 in the table. 



42 



The Treatment of Steel 



The same bar twice hammered cold, after anneahng, was 
reduced to 0.624 inch in diameter; this is No. 3 in the 
table. 

The same bar annealed, and hammered cold four times, 
was reduced to 0.564 inch in diameter; this is No. 4 in the 
table. 

Table IV 

Drill Rod Samples 













Diff. 








3 


Diff. 


3-4 
Effect of 


Nos. 


I 


2 


Sp. Gr. 


3-2 




Sp. Gr. 


Sp. Gr. 


Scaled and 


Effect of 


Scale off in 








not Hardened 


Hardening 


I and 2 


I 


7.8068 


7.818 


7.829 


— .01 r 


+ .022 


2 


7794 


7.812 


7.828 


— .016 


+ ■034 


3 


7.816 


7.790 


7.8r7 


—.027 


+ .001 


4 


7.787 


7765 


7.780 


-.0,5 


—.007 



Prof. Langley first took the Sp. Gr. of the four pieces as 
he received them, i and 2 having the roll scale upon them, 
and 3 and 4 being bright polished, all having been boiled in 
dilute potash and slowly cooled. The results are given in 
column No. i. 

In this case No. 3 indicates an increase of Sp. Gr. due to 
the cold hammering. Prof. Langley then, thinking that the 
results might have been affected by scale in the first two 
pieces, next removed the scale and boiled them all in weak 
potash, and upon removing them from the boiling liquid 
cooled them rapidly by plunging them quickly into cold water. 

Column No. 2 gives the results, and here we have the 
remarkable fact that sudden cooling from boiling temperature 



IVhy Does Steel Harden ? 43 

causes a hardening effect, which is shown more particularly 
in Nos. 3 and 4, where there is a decided reduction of 
Sp. Gr. 

If subsequent trials prove this deduction to be correct, it 
is very important. Desiring to fortify himself as to this 
matter of hardening at such a temperature. Prof. Langley 
again boiled the pieces and allowed them to cool very slowly, 
thus annealing them. The results are given in column No. 3. 

Here is a progressive reduction of Sp. Gr., showing that 
cold hammering as well as cold rolling reduces Sp. Gr. The 
restoration of the Sp. Gr. of 3 and 4 to the results in column 
No. I shows that there was a hardening due to quenching 
from boiling temperature. The column of differences 3 and 

2 shows the effect of hardening. The column of differences 

3 and I shows the effect of removing the scale. This column 
also accounts for the increase of Sp. Gr. shown in the 
"restored" or annealed pieces of No. i, Table I, recorded 
in Table III. The results recorded in Table IV have an 
important bearing on the inquiry into the cause of hardening, 
which will be shown later. They are also important as 
showing the entirely mercurial or thermometric nature of 
steel. They also indicate a mode of accurate determination 
of the variable rate of change of volume in steels of different 
composition. 

It will be remembered that there is such a variable rate 
of change clearly shown in Table I, and further evidence 
will be given in Table V. 

Now, by operating upon different samples by boiling, and 
sudden cooUng in water of uniform temperature, we can get 
results which will range between certain uniform and known 
temperatures for each experiment. 



44 



The Treatment of Steel 



This is an experiment to find by measurement the effect 
of repeated hardening upon three pieces of steel containing 
different amounts of carbon. 

A hole about .75 inch in diameter was drilled in the 
middle of each piece. The measurements were taken by 
means of a tapered plug, the difference in the distance to 
which it entered in each case, after the first and subsequent 
hardening, being measured by micrometer. The left-hand 
columns give the numbers of the successive hardenings. 
The other columns show the changes in the diameter of the 
hole. The first piece, of carbon .848, showed contraction 
of the hole every time it was hardened except the sixth, 



Table V 
Changes in Volume by Repeated Hardening 



No. of 
Times 


Nos. 6 and 7, 

Table 1 
C = about .848 


No. 4, Table I 
C =.649 


No. 3, Table I 
C =.529 


Hardened 


Contraction of 
Hole 


Expansion 


Contrac- 
tion 


Expansion 


Contrac- 
tion 


I 

3 
4 

I 

7 


.00172 
.00172 
.00688 
.00688 
.00688 
.00000 
.30044 crack'd 


.00172 
not cracked 


.00257 
.00086 
.00482 

.00172 
.00000 


.... 

.... 

.00173 

.00086 

.00086 

not cracked 


.00086 
.00172 
.00000 

.00086 


Total ) 
change \ 


.02752 




.00771 


.00000 


.00000 



Hole was originally .75 diameter 



IVbv Does Steel Harden ? 45 

and the piece cracked at the seventh hardening. The 
operator supposes the sixth hardening was accidentally 
omitted. 

The second piece, of carbon .649, showed contraction 
three times, then no change. Then an expansion of the 
hole followed by a contraction, and the seventh time there 
was no change. This piece did not crack. 

The third piece, of carbon .529, showed two contractions, 
then no change, followed by three expansions, and seventh 
a contraction. This piece did not crack. 

The total changes are quite marked : 



Showing for carbon (S48 = .02752 inch 

Showing for carbon 649 = .00771 inch 

Showing for carbon 529 = .00000 inch 



This shows in another way that steel of high carbon 
changes more in volume per degree of temperature than 
steel of low carbon. 

The high steel cracked, the low did not. All the pieces 
were of the same quality. 

The experiment recorded in Table No. V forms no part 
of the investigation by Prof. Langley and ourselves. It was 
made rather crudely for a practical purpose, and the results 
obtained in practice confirm the figures in the table. 

This ends our record of facts and brings us to — 

4. A statement of some of the theories which have been 
given as the cause of hardening. 

Perhaps the oldest, one of the most plausible, and possibly 
the true reason, is that unhardened steel contains carbon in 



46 'The Treatment of Steel 

graphitic and uncombined form, and hardened steel has its 
carbon all combined. 

For proof it is stated that when unhardened steel is 
dissolved, the insoluble residue contains flocculent graphitic 
carbon ; and when hardened steel is dissolved it leaves no 
residue of carbon ; therefore, the carbon has been combined 
in the hardening. To answer the objection to this, that it is 
impossible for iron and carbon to combine in all proportions, 
one writer states that there is formed a definite carbide FeC^. 

That this carbide is excessively hard, and that it acts as a 
cement or glue, and therefore the high carbon steel becomes 
so much harder than the low carbon steel. 

This will be conclusive after the carbide has been sepa- 
rated and thoroughly examined. Meantime, the hardening 
from boiling temperature is a little puzzling. 

Another writer states that solution of the carbon takes 
place when the steel is heated, and that a great compression 
caused by the sudden contraction in cooling is the cause of 
hardness. 

If this be so, and our experiments are correct, then carbon 
dissolves in steel at the temperature of boiling water. 

One writer hastens to inform us that steel hardens because 
part of the carbon is burnt out in heating, and the rest of the 
mass is compressed by the sudden cooling. It might afford 
amusement to demolish this theory, if it would not be a waste 
of time. 

A steel maker of twenty years' practice says hardening is 
caused by the carbon assuming the diamond form, in very 
minute crystals. 

He gives as a proof, that the hot steel decomposes water, 
or the cooling mixture, which always contains hydrogen. 



fVhy Does Steel Harden ? 47 

The hydrogen combines with the carbon to form dia- 
monds, and this is proved by the fact that the diamond and 
hardened steel both refract light. 

In case water is the cooling medium, the hydrogen pene- 
trates the steel to form diamonds, while the freed oxygen, 
conveniently inert, stays on the outside to form a thin film 
of oxide. 

As it is well known that mercury is one of the very best 
cooling liquids, giving extreme hardness to steel, it is 
necessary to this theory to show that mercury contains 
hydrogen. 

Again, if steel really hardens upon being quenched from 
boiling temperature, then water must be decomposed by that 
temperature. 

This diamond theory is very attractive, and has received 
much consideration in our minds, but we are not prepared 
to consider it proven. 

Another writer states that hardening is due to the sudden 
arresting of the molecular motion that exists in the heated 
steel, thus causing great tension and resulting hardness. 
He offers, as proof, that hardened steel is weaker and more 
brittle than unhardened steel, and cites as a very happy 
illustration the case of hardened glass which is known to be 
in a high state of tension. This theory tallies with all the 
facts better than any we have seen. 

First, it covers all conditions, from the boiling tempera- 
ture up to the high yellow heat which causes intense hardness 
and the brittleness of glass. 

Again, it is certain that the higher the heat the greater 
the molecular motion. Also it is certain that from the highest 
heat we get the greatest hardness, and the greatest brittleness. 



4 8 The Treatment of Steel 

Finally, the restoration of grain, and of Sp. Gr. by 
annealing, agree well with the idea of tension in one case, 
and the relief from tension in the other. 

It is possible, even if this tension theory be accepted as 
correct, that there may be, in connection with it, a change 
to diamond form, or from graphitic to combined carbon, and 
the formation of a definite carbide. Some one of these 
changes, taking place at a given temperature, may be just 
what is needed to explain that very remarkable phenomenon 
known as "refining." 

In mentioning a few practical considerations to be drawn 
from what has been said, it is hardly necessary to address 
the unfortunate smith and temperer ; they, poor fellows, 
have heard so much of uniform heating and low heating, 
that they may well feel heart-sick, and determined to do as 
they please anyhow. 

Let them do as they will, they will never be allowed to 
forget that same old cry — "too much heat" — "irregular 
heat " — and so on. 

Let that cry continue ; it has its uses ; and let us look at 
the engineer's side. 

As steel advances with irresistible steps into the field of 
construction, the engineer naturally asks — What am I to do 
with it ? 

Can it be worked safely ? 

Is it reliable? 

Shall I use high steel or low .^ 

How is it to be worked ? 

Is it safe to use the apparent advantages of great 
strength to be had in high steel ? 

Is it necessary to anneal finished work? etc., etc. 



Why Does Steel Harden ? 49 

We think it has been clearly shown — 

1. That a good soft heat is safe to use if steel be 
immediately and thoroughly worked. 

It is a fact that good steel will endure more pounding 
than any iron. 

2. If steel be left long in the fire it will lose its steely 
nature and grain, and partake of the nature of cast-iron. 

Steel should never be kept hot any longer than is neces- 
sary to the work to be done. 

3. Steel is entirely mercurial under the action of heat, 
and a careful study of the tables will show that there must 
of necessity be an injurious internal strain created whenever 
two or more parts of the same piece are subjected to 
different temperatures. 

4. It follows that when steel has been subjected to heat 
not absolutely uniform over the whole mass, careful anneal- 
ing should be resorted to. 

5. As the change of volume due to a degree of heat 
increases directly and rapidly with the quantity of carbon 
present, therefore high steel is more liable to dangerous 
internal strains than low steel, and great care should be 
exercised in the use of high steel. 

6. Hot steel should always be put in a perfectly dry 
place of even temperature while cooling. A wet place in 
the floor might be sufficient to cause serious injury. 

7. Never let any one fool you with the statement that 
his steel possesses a peculiar property which enables 
it to be "restored" after being "burned;" no more should 
you waste any money on nostrums for restoring burned 
steel. 

We have shown how to restore "overheated" steel. 



50 The Treatment of Steel 

For " burned " steel, which is oxydized steel, there is 
only one way of restoration, and that is through the knobbling 
fire or the blast furnace. 

"Overheating" and "restoring" should only be tried 
for purposes of experiment. The process is one of disinte- 
gration, and is always injurious. 

8. Be careful not to overdo the annealing process ; if 
carried too far it does great harm ; and it is one of the com- 
monest modes of destruction which the steel maker meets in 
his daily troubles. 

It is hard to induce the average worker in steel to believe 
that very little annealing is necessary, and that a very little 
is really more efficacious than a great deal. 

Finally, it is obvious that as steel is governed by certain 
and invariable laws in all of the changes mentioned, which 
laws are not yet as clearly defined as they should be, nor as 
they will be ; nevertheless, the fact that there are such laws 
should give us confidence in the use of the material, because 
we may be sure of reaching reliable results by the proper 
observance of the laws, therefore there is no good reason 
why engineers should be afraid to use steel if they manipulate 
it intelligently. 

Now, if we have wandered over a wdde range in answer 
to the simple question — " Why does steel harden ? " — it was 
necessary to have looked at many facts before we could 
have an intelligent opinion of many theories ; and if any are 
in doubt as to what is the correct answer to this momentous 
question, we can only say that we are all in the same boat, 
for if you do not know, neither do we. 



Hardening and Tempering Steel 

From a work by George Ede, 
Woolwich Arsenal, England 

We have now arrived at a very important process, justly 
termed the crowning process. It is that of hardening the 
articles ; and, if the proper steel has not been chosen for 
the articles, or if the proper steel has been chosen and has 
not afterward been properly treated through all the stages 
which it has had to pass, or if the hardener be not fully 
aware of the general principles upon which he must proceed, 
all past efforts may prove futile. It is not requisite that the 
hardener should be a chemist; but some slight acquaintance 
at least with chemistry, or of the action of substances upon 
each other, will be extremely serviceable to him. To be 
unqualified in this respect will be laboring in the dark : a 
successful result may often be obtained ; but it will be very 
imperfectly known how it happened, and it will afford no 
valuable instruction for the future. 

There are too many who entertain an opinion that they have 
nothing new to learn lohich is worth notice; they are apt, in 
effect, to say, that, having served an apprenticeship to their 
business, they ought to know something, and because they 
ought to know something, they seem to expect submission 
to their very errors. To such I speak not ; to convince 
them would be impossible, and therefore the attempt folly. 
But the prudent artisan, whose first care is generally to pro- 
vide himself with tools adapted to his labors, I would ask to 
improve his knowledge of that material, the proper choice 



^2 The Treatment of Steel 

and management of which constitutes the first step toward 
success in mechanical pursuits. 

The art of hardening and tempering steel constitutes one 
of the most delicate, curious, and useful branches connected 
with mechanical art; it is an art of long standing, and always 
one of anxiety, but by whom or when it was first adopted I 
am not prepared to decide. At first sight it appears suffi- 
ciently simple, when by healing a piece of steel to redness, 
and plunging it into cold water, it becomes hard ; on a closer 
inspection, however, the mind will soon discover that many 
operations and contrivances require to be carried into effect 
by the hardener in order to become efficient in his art, or to 
be distinguished for skill and promptitude in execution. A 
slight knowledge of the processes will also discover that a 
certain amount of patient perseverance is required — an 
amount of which few who have been brought up at the desk, 
or behind the counter, can form the slightest idea. But I 
have not set out with the object to discourage the young 
practitioner, but rather to encourage him and smooth for him 
the path which I have myself found so rough, but which I 
have always endeavored to explore without entertaining a 
sentiment of its hardship; and I would advise all young men 
who are just starting in the world to go and do likewise. 

Before proceeding further, 1 would state, that 1 have not 
undertaken to explain everything in connection with this 
subject; but my main object in the present chapter is to 
explain, in a plain way, the chief causes why steel breaks in 
hardening ; also to notice some of the contrivances which I 
have found in my own experience to be the least expensive, 
and most easily reducible to practice ; the most suitable to 
prevent steel from breaking; and, if the information be 



Hardening and "Tempering Steel 53 

properly studied, it will enable the mechanic to harden and 
temper any kind of article with which he may have to do. 

Many theories upon the cause of steel becoming hard by 
the process of heating and suddenly cooling it have been 
formed; but they are so beset with difficulties and uncer- 
tainty, that in my opinion the proper cause has not yet been 
proved. I have previously shown that steel is a compound 
of iron and carbon ; and, as pure iron does not harden by 
simple immersion, it must be to its carbon that steel owes 
this valuable property ; and, if I may be allowed to theorize 
on the reason why steel becomes hard by sudden cooling, I 
should be inclined to state that it is the crystallization of the 
carbon, caused by compression and sudden cooling, and, 
being combined with the iron, becomes a hard and solid 
substance; but, let this be so or not, there is one thing 
certain, that a new arrangement of the particles takes place 
by the process of hardening. But, as I shall have an 
occasion to speak upon this hereafter (in the chapter upon 
the expansion and contraction of steel), it will be superfluous 
to speak upon it in this place, but rather confine myself to 
the mechanical operations of the subject. 

It is of considerable importance that the designer of tools 
or other articles should have some knowledge of the quality 
of the material to be used ; likewise he should have some 
knowledge of the action of fire and water upon the material ; 
also he should have some knowledge of the practice of the 
hardener. 

The workmen, through whose hands the articles must 
pass, either in the fitting or the turning room, should also 
have some knowledge of the art of hardening ; in fact, it is 
as requisite that fitters and turners should have some knowl- 



54 '1'^^ Treatment of Steel 

edge of the practice of the hardener and the action of fire 
and water upon the steel, as it is for the pattern maker to 
have some knowledge of the practice of the molder. 

The superior character of castings depends in a great 
measure upon the superior skill which has been displayed 
upon the patterns ; and the success in the hardening of 
steel, in many instances, depends in a great measure upon 
the ingenuity displayed in the fitting or the turning 
room, and also on the ingenuity displayed in designing the 
article. 

Too little attention is generally paid to the quality of the 
material when required for very particular tools, or, in other 
words, for tools that require a great amount of labor and 
time to make them ; and in the fitting or the turning room, 
or even in the drawing office, the expansion and contraction 
of steel is seldom heeded or even thought of, though it is of 
the greatest importance. 

When it is required to make an expensive article, and 
where there is great risk of its breaking in the hardening, 
the first thing to be done is to select the proper steel for the 
purpose and afterward to anneal it to the fullest extent ; if 
an equal and judicious hammering be given to the steel by 
the smith before it is annealed, it gives a density to the 
steel, and the article will be more durable ; besides, it will 
lessen the risk of its breaking in the hardening, but the 
effect of the hammering, as I have before remarked, is taken 
off again by strong ignition, and the smith's labor is lost ; 
therefore it is evident that there is as much care required in 
heating the steel when it is required to be annealed as there 
is in heating it when it is required to be forged or hardened. 
When the steel is annealed it is then in a fit state for the 



Hardening and Tempering Steel ^S 

fitting or the turning room, there to be fashioned into the 
required article. 

The artist employed upon it ought to bear in mind that 
steel breaks in hardening from its unequal contraction at 
different parts ; the danger increases with the thickness and 
bulk, and the more especially when certain parts are une- 
qually thick and thin, consequently before finishing any 
article for hardening one thing should be attended to, which 
I will attempt to explain, and, if I succeed in making it 
understood, the artist \\\\\ have obtained information as to 
the plans to be adopted with large articles generally. It is 
this : examine the article and see which part of it is likely 
to be the last to become cold when it is immersed in the 
water, and if it is practicable to reduce the steel in that part 
without inconveniencing the article it is advisable to do so ; 
the steel will then cool more uniformly and be less liable to 
fracture. If it were possible to get every particle of the 
steel cold at the same moment, there would be an end to the 
danger of steel breaking in hardening; but as this cannot 
be done, we must approach it as near as we can. 

For the better understanding of the subject, let us sup- 
pose that a large circular cutter, such as are used for shap- 
ing and truing of work of various shapes, is required to be 
made. We will suppose it to be required about 7 inches 
in diameter and 2 inches in thickness, with numerous cut- 
ting edges (termed teeth) round the circumference, and a 
round hole in the center through which to pass the spindle. 
It is obvious that the first thing which will require to be 
done will be to select the proper steel for the cutter and 
afterward to forge it to the required dimensions, after which 
it will require to be annealed to the fullest extent ; but as 



^6 The Treatment of Steel 

the choosing, forging, and annealing have already been 
treated of, it will be superfluous to speak more upon it in 
this place, consequently, let us suppose the steel in its forged 
and annealed state to be obtained. The first thing usually 
done after the steel is obtained is to bore the mandrel hole, 
after which it is turned to the required thickness, and the 
two sides of the block of steel left flat ; the superfluous 
metal upon the circumference is then turned ofl", which 
leaves the block of the required diameter. The teeth are 
now cut upon the circumference of this block of steel, either 
by means of a file or by a tool whose edge is of the proper 
form, and can be used either in a planing or shaping 
machine, or even with the lathe. But the most perfect teeth 
are cut by means of another rotary cutter, whose edge is of 
the proper form, and working in a machine constructed for 
the purpose. It is usual to bore the mandrel hole in large 
cutters the same size as the mandrel hole in the smaller size 
cutters, so that both large and middle-size cutters may fit 
the same mandrel, but this is a step in a wrong direction. 
The larger the cutter the larger the mandrel hole should be 
— not to say that the mandrel itself would not be strong 
enough ; but a large mandrel hole in large cutters favors the 
cutters in hardening by allowing the steel to cool more uni- 
formly ; whereas a small mandrel hole in a large cutter, hav- 
ing two plain flat sides or surfaces, increases the risk of the 
cutter breaking in hardening. Though a large mandrel hole 
favors a large cutter in hardening,- still it is not absolutely 
necessary to have a large mandrel hole in them, because 
large cutters having a small mandrel hole in them may be 
hardened without breaking them, by taking care previous to 
hardening them to reduce the substance of the steel. 



Hardening and Tempering Steel 57 

The substance of the steel must be reduced in that part 
of the cutter which is the last to become cool when it is 
immersed in the water. It is obvious that the part which is 
the last to become cold will be half way between the man- 
drel hole and the circumference, consequently large cutters 
will require to be dished out or turned concave on both sides ; 
or if a few smaller holes than the mandrel hole be bored round 
the mandrel hole, it will answer the same purpose as turning 
each side concave. Either of the above plans will greatly 
reduce the risk of all large cutters breaking in hardening, 
and it does not materially reduce their strength or stability. 

It is obvious that the method of turning the sides of 
large cutters concave cannot be adopted with cutters which 
require to have teeth on their sides as well as on their cir- 
cumference ; still holes could be bored through these, and 
probably it would not in the least prevent the cutter from 
doing its work ; still the cutter would not have a very pleas- 
ing appearance, and it would not look very mechanical. 
Consequently, instead of boring holes in these kinds of 
large cutters, it will be better to make the mandrel hole 
large in proportion to the cutter. 

Perhaps it will be of some use to hint, as it is a very 
valuable hint if properly taken, that a circular cutter of any 
required thickness, and 7 inches in diameter, and which 
has a 3-inch mandrel hole through its center, is less liable 
to break in hardening than a circular cutter of the same 
thickness, 6 inches in diameter, and which has a 2-inch 
mandrel hole through its center. 

There are numbers of articles besides cutters which re- 
quire to be hardened, where it becomes necessary to bore 
holes in them, or cut out a kind of panel to make them cool 



58 The Treatment of Steel 

more equally. In some instances boring holes in steel arti- 
cles requiring to be hardened is injurious or unfavorable to 
the articles in hardening. For instance, boring holes too 
near the outside edges of some kinds of articles will some- 
times cause the article to crack at the hole. 

It may be well to state that drilling a hole or center too 
large or too deep into screw taps or reamers, and various other 
articles which require to be hardened, is a great evil and 
should in general be avoided ; for, when the centers are 
too large or too deep, it weakens the ends of the articles, 
and it not only weakens the ends of the articles, but it fre- 
quently causes a fracture in the steel at the bottom of the 
center. 

In all cases, if the centers are not required in the articles 
after they are hardened, it is advisable to file them out pre- 
vious to hardening them, and thus prevent all risk of their 
getting cracked at that part in hardening. 

In making steel tools or steel articles of any description 
sharp internal angles should in general be avoided, as they 
are very unfavorable in the hardening process ; consequently 
the key ways in cutters should be half circle. In all kinds 
of articles sharp internal angles are unfavorable to the 
strength of the articles, so that it becomes necessary to leave 
all the internal corners a little rounded. 

It may be useful, perhaps, to add that cutters which are 
required for cutting soft substances, such as brass or copper, 
require to have their teeth very sharp, and to be made very 
hard. The teeth require also to be cut much coarser than 
for iron or steel, otherwise they soon become choked with 
the metal, and become hot, and very soon lose their sharp 
edges, and will not cut, as the term is, sweet, but would 



Hardening and Tempering Steel 59 

polish and glide over the metal almost without effect, were 
the cutters not seconded by a great amount of power. 

When a steel tool or piece of work similar in shape to a 
piece of a bar of round steel, say, 2, 3, 4, or more inches in 
diameter, and 3, 4, 5, or more inches in length, is required to 
be hardened, it frequently becomes necessary, previous to 
hardening such a tool or piece of work, to bore a hole through 
the center of it, in the direction of its length, in order that the 
water may pass through the hole, and cool the steel more 
equally, and reduce the risk of its breaking. But as the two 
ends are even then always likely to become cool first, it would 
not be amiss to widen the hole a little more in the center 
than at the ends, and so further reduce the risk of its break- 
ing in hardening. 

It is unnecessary, perhaps, to remark, that the largest 
size screw taps and hobs are very liable to break in harden- 
ing, and, though a hole might be bored through them to 
prevent their breaking, still this would not give a very 
pleasing appearance, nor would it look very mechanical. 
Independent of the appearance of the tap or hob, a hole 
through large screw taps or hobs would be very apt to cause 
them to become oval in hardening; and if this did occur it 
would cause the tap, when in use, to make the hole larger 
than it was intended to do, and cause the hob when in use 
to cut very unequally and very slowly, because only two 
opposite sides of the hob could be made to cut. 

It is obvious that a round piece of steel having a plain or 
smooth surface, and which has a hole bored through it in 
the direction of its length, would be as likely to become 
oval in hardening as a piece of steel having a similar hole 
through it and a screw upon its surface, such as a tap or hob. 



6o The Treatment of Steel 

But then there are means by which a plain surface can be 
made true again after hardening, such as by lapping or 
grinding, whereas with taps or hobs these methods cannot 
be adopted. In all cases it must be borne in mind that, the 
more uniformly articles are heated, the less liable are they 
to become crooked or oval in hardening. 

For the various reasons above given, another method 
differing from the boring of holes through large taps or hobs 
may be adopted, a method which will not at all disfigure the 
taps or hobs, or cause them to become oval, but which will 
cause them to harden and cool more uniformly, at the same 
time prevent them breaking. It is this : to turn the plain 
part of the tap or hob as small as it will conveniently bear 
without encroaching upon the required strength of the tap 
or hob, and to cut the concave grooves (which are in the 
direction of the lengths of the best kind of taps) a little 
deeper than what they are generally cut. 

The method of reducing the steel in that part of large 
articles which is the last to become cold when they are 
immersed in the water, cannot with some kinds of articles be 
adopted ; because, were the steel to be reduced in that 
particular part, it would unfit the articles for the purpose for 
which they are intended. This would be the case with large 
circular dies, which frequently require to be turned flat on 
both sides. It is obvious that the method of boring holes 
through these kinds of articles, or turning the sides of them 
concave, cannot be adopted ; consequently another method 
must be resorted to. It is this : to heat an iron ring or 
collar, and while the die is in a cold state shrink the heated 
ring tight upon the die; this method will, when the die is 
heated and immersed in the water, lessen the risk of fracture. 



Hardening and Tempering Steel 6i 

It will be imagined, perhaps, that the object of shrinking 
a ring upon the die is to compress the die, and by compress- 
ing the die it will keep it from breaking ; now, if this were 
the object, it would be a step in the wrong direction. The 
object of shrinking a ring upon the die is to prevent the 
water from cooling the outside of the die too suddenly. It 
must be borne in mind that the more suddenly the heat is 
extracted from the steel, the more sudden is the contraction 
of the surface steel ; and the more sudden the contraction of 
the surface steel, the more sudden and greater is the com- 
pression of the interior steel ; and the more sudden and 
greater the compression of the interior steel, the greater is 
the risk of the steel breaking by the outer crust being held 
for the moment in a greater state of tension (strain). The 
more the interior steel is compressed the more dense it be- 
comes ; consequently, when it becomes cold it occupies less 
space than what it occupied previous to hardening, and the 
result is an internal fracture. 

It will not be out of place, perhaps, to remark that if 
every mechanic were made more acquainted with the chemi- 
cal properties of the material, and the action of fire and 
water upon the material, thousands of articles which have 
been thrown aside might have been prevented from being 
burnt in forging, and thousands more would have been saved 
from being cracked in hardening ; and the price paid upon 
the forging, annealing, turning, fitting and hardening, or 
making articles from bad material, might have been saved. 

Suppose a similar block of steel to the one just treated 
of to be required for a large friction wheel, the method of 
shrinking a ring upon it previous to hardening of it will not 
answer, because the ring would prevent the water from effec- 



62 The Treatment of Steel 

tually hardening the steel in that part which is required the 
hardest ; consequently the same methods will have to be 
adopted with this kind of article as those which are to be 
adopted with a large circular cutter, either boring holes 
through it or turning the sides concave. Suppose an eccen- 
tric steel collar is required to be hardened, for example. 
Let us suppose the hole in the collar where the shaft or man- 
drel passes through to be about two inches in diameter, and 
the thickness of the metal one inch and a half on one side 
and about the quarter of an inch on the opposite side ; from 
the irregular form of this article it will easily be seen that 
there is great risk of its breaking in hardening. The unequal 
thickness of the steel causes unequal contraction, one side of 
the collar being so thin it is cool almost instantly. The stout 
side contracts after the thin side is fixed ; the thin side in its 
then hard state cannot give ; consequently it breaks. Before 
such an article as this is sent to the hardener, a piece of iron 
should be fitted to the thin side of it, so as to make both 
sides about equal in thickness. The iron must be fitted to 
the inside, as it is the outside of the collar which is required 
hard. This piece of iron is to prevent the thin part of the 
collar from cooling too suddenly, and thus prevent the col- 
lar breaking. The piece of iron, of course, must be bound 
upon the collar with a piece of binding wire, after which it 
is ready for hardening. I may here remark that a square 
lump of steel is less liable to break in hardening than either 
a cylindrical or spherical lump, even though there be more 
bulk in the square lump than what would form either the 
spherical or the cylindrical lump. 

Although this is such an important subject, and much 
more might be said, still it is not necessary, perhaps, to en- 



Hardening and Tempering Steel 63 

large more upon it, as the mind will have discovered by this 
time the method of proceeding with tools or articles of any 
description requiring a great amount of labor and time to 
make them ; and where there is great danger of their break- 
ing in hardening. The same or similar methods will have to 
be adopted in all cases where large masses of steel require to 
be hardened, if we wish to obtain satisfactory results. 

The information here afforded, coupled with the work- 
man's own experience and ingenuity, will doubtless be suffi- 
cient to prevent his finding difficulty in forming for himself 
any particular idea upon the subject he may want; conse- 
quently I will now pass on to the process of hardening and 
tempering. 

In the process of hardening steel, water is by no means 
essential, as the sole object is to extract its heat rapidly, and 
the more sudden the heat is extracted, the harder the steel 
will be; consequently, those substances which act most sud- 
denly upon the steel will produce the greatest effect, though 
they will not always produce the most satisfactory results, 
for intense cold has a very unfavorable effect upon steel. 
Good cast-steel receives by sudden cooling a degree of 
hardness almost equal to that of the diamond, and almost 
sufficient to cut, or make an impression upon, every other 
substance ; and, when of the best quality, and the hardness 
not carried to extreme, a certain amount of tenacity is also 
combined with the hardness. 

If steel is heated to a red heat, and allowed to cool 
gradually, it becomes nearly as soft as pure iron, and may, 
nearly with the same facility, be worked into any required 
form. If steel be too hard, it will not be proper for tools, 
or instruments of any description, which are required to 



64 'rhe IWeatment of Steel 

have very keen edges, or very fine points, because it will be 
so brittle that the edges will soon become notched, or the 
points break off on the slightest application to the work ; if, 
on the contrary, the steel be too soft, the edges or points 
wdll turn or bend ; but, if the steel is duly tempered, it will 
resist breaking on the one hand and bending on the other. 

The degree of heat required to harden steel is different 
in the different kinds. The best kinds require only a low 
red heat; the lowest heat necessary to effect the desired 
purpose is the most advantageous, and to impart to it any 
extra portion of heat must partly destroy its most valuable 
properties ; and for this misfortune there is no remedy, for, 
if cast-steel is overheated, it becomes brittle, and can never 
be restored to its original quality ; therefore, it will be quite 
incapable of sustaining a cutting edge, but will chip or 
crumble away when applied to the work. 

There are various ways of applying the heat to articles 
when they require to be hardened. The methods to be 
adopted will of course depend upon the shape and size of 
the articles ; also upon the quantity requiring to be operated 
upon, for in some instances a large quantity can be heated 
and hardened as expeditiously as a single article. Some- 
times it is requisite to heat the articles in the midst of the 
fuel in a hollow fire : sometimes it is requisite to heat them 
in an open fire ; and sometimes it is requisite to inclose and 
surround them with carbon in a sheet-iron case or box, and 
heat the whole in a hollow fire or in a suitable furnace ; at 
other times, or in some instances, it is more convenient to 
heat them in red-hot lead When a large quantity of some 
kinds of articles is required to be hardened, the method of 
heating them in red-hot lead is very convenient and very 



Hardening and Tempering Steel 6^ 

economical ; but to be constantly employed dipping articles 
in red-hot lead is, I believe, very injurious to health. I have 
myself been so employed, and have felt its very bad effects ; 
and I have, therefore, avoided using it as a source of heat 
except in cases of great necessity. 

A more uniform degree of heat can be given to some 
articles by heating them in red-hot lead than by any other 
means, especially some kinds, which are of great length ; 
consequently, they will keep their proper shape better in 
hardening. A gas tiame, or the flame of a candle, is very 
convenient for heating the point of some small articles ; 
some small articles may be sufficiently heated by placing 
them between the red-hot jaws of a pair of tongs. Some 
small articles may be heated by taking a piece of bar iron, 
and, after heating it to redness, cutting it half-way through 
with the chisel, and then placing the articles in the nick, 
which will heat them sufficient for hardening. Sometimes 
it is necessary to insert a piece of iron pipe in the midst of 
the ignited fuel of the fire, and then to place the articles in 
the pipe. 

When a large number of steel articles are required to be 
hardened all over, or throughout their body, and which are 
too small to be heated in the midst of the ignited fuel of a 
hollow or open fire, and perhaps it is inconvenient to heat 
them in red-hot lead, or if it be thought hazardous to enclose 
them entirely in a sheet-iron box, from an apprehension that 
the heat might increase too much, the following scheme may 
be adopted. Place as many of the articles at once as may 
be convenient to manage into a sheet-iron pan, without a 
lid, and cover them with charcoal dust ; place the whole in a 
furnace or hollow fire, and slowly heat them to redness. 



66 The Treatment of Steel 

They should be occasionally and carefully moved about in 
the pan by the use of a small wood or iron rod, in order to 
equalize the heat ; the charcoal dust prevents the articles 
from scaling so readily, and has a tendency to prevent the 
rod bending them when moving them about in the pan. 
When the articles arrive at the proper heat they may be 
immersed in water or oil, or water with a film of oil upon 
the surface, according to the degree of hardness required 
in them. 

A rod of good steel in its hardest state is broken almost 
as easily as a rod of glass of the same dimensions, and this 
brittleness can only be diminished by diminishing its hard- 
ness ; and in this management consists the art of tempering. 
The surface of the hardened steel is brightened, and it is 
exposed to heat. As the heat increases there is a curious 
and uniform change in the clear color of the surface. The 
colors which appear upon the surface of the steel are sup- 
posed to be the result of oxidation. The thickness of the 
coat or film of oxide, if such it be, determines the color, and 
the thickness of the coat depends upon the temperature to 
which the work is exposed. 

It is quite probable that these colors are the result of 
oxidation ; but the present state of my knowledge does not 
enable me to prove that these colors would not appear if the 
steel could be heated in a vacuum, a space unoccupied with 
air, neither does the present state of my knowledge enable 
me to prove that these colors are not due to the new ar- 
rangement of the particles, quite independent of any chem- 
ical change ; but, let the cause be what it may, these colors 
are a very useful index, for by them any degree of hardness 
retained by the steel may be ascertained. The colors which 



Hardening and Tempering Steel 67 

successively appear on the surface of the steel, slowly heated, 
are a yellowish white or light straw color, a dark straw, gold 
color, brown, purple, violet, and deep blue. Finally, the 
steel becomes red hot, and a black oxide is formed. It will 
be more readily imagined that the various colors are the 
result of oxidation, when it is seen that the action of the 
oxygen of the atmosphere upon the steel in a red-hot state 
converts the surface of the steel into a black oxide ; and 
this black oxide, like the various colors, increases in thick- 
ness with increase of temperature, and if it is hammered or 
scraped off it is again quickly formed. 

There are various ways of applying the heat for temper- 
ing or reducing the hardness in steel articles. The methods 
to be adopted wdll, of course, depend upon the shape and 
size of the articles ; also upon the quantity requiring to be 
operated upon ; for in some instances a large quantity can 
be tempered as expeditiously as a single article. The heat 
for tempering should not be too suddenly applied, as a cer- 
tain amount of time is essential for the particles to rearrange 
themselves, and the slower the heat is applied the tougher 
and stronger the steel becomes. When it is required to 
temper an article or articles to any of the colors previously 
spoken of, they must be brightened after they are hardened. 
But before proceeding farther it will perhaps be well to state 
that previous to brightening the articles the hardener ought 
always to make himself sure that the articles are quite hard. 
If the articles are not properly hardened, or, in other words, 
if the articles are not possessed of a certain degree of hard- 
ness, it will be time and labor lost afterward to temper them ; 
besides, the articles will be practically useless for the pur- 
pose they are intended for until they have been hardened 



68 The Treatment of Steel 

and tempered over again. Therefore, in order to make sure 
of good work, the hardener shoukl always try the hardness 
of the steel with a smooth file, a file finely cut. It has 
already been inquired of me, and may be inquired again, 
perhaps, why is it necessary for a practical man who is thor- 
oughly acquainted with the quality of the material he is 
hardening, likewise with the temperature suitable to harden 
the material, to try the hardness of the steel, when he knows 
from experience that the steel hardens properly at a certain 
temperature t The answer to this is, the hardener may be 
a practical man, and may be thoroughly acquainted with the 
quality of the material, likewise with the temperature suit- 
able to harden the material ; but if he is not a careful man 
his knowledge will be of little service, and the necessity for 
trying the hardness of the steel before it is tempered is soon 
made evident; besides, if proper attention is not paid to the 
water it will deceive the hardener. Again, the most careful 
and experienced hardener is liable to be deceived in the 
temperature of the steel when hardening in twilight. It has 
previously been stated that it is requisite at times to enclose 
some kinds of articles, when they require to be hardened, in 
a sheet-iron box, and surround them with charcoal. When 
this method is adopted, the articles will require a much 
more considerable amount of time to heat them than is 
readily imagined by those who are not accustomed to this 
method. Charcoal is a bad conductor of heat, and if the 
hardener be unacquainted with the conducting quality of the 
charcoal, he will be apt to draw the box out of the fire and 
immerse the contents in the water before the central articles 
have acquired the proper temperature suitable for hardening 
them, and those articles which are below a certain heat 



Hardening and Tempering Steel 69 

cannot become hard. Here again is exhibited the necessity 
of trying whether all the articles are hard before beginning 
to temper them. In some instances (though the steel be the 
very best that Sheffield can furnish), one or two badly 
tempered articles would get the manufacturer of them a bad 
name, and would in some instances get all the order con- 
demned, even if all the other articles were right. The use 
of the file for proving whether the articles are hard can be 
dispensed with when the articles are brightened on an emery 
wheel, or a small dry grinding stone running at a quick 
speed, for the person employed to brighten them will find, 
if they are properly hardened, plenty of brisk, lively sparks 
fly from them when they are held upon the emery wheel or 
the grinding stone. But if they are not hard there will 
be very little fire in them. Therefore, with a very little 
attention, these articles which are soft (if any there be) can 
be detected, and may be put aside and heated again with 
the next batch. 

After the articles are brightened, the hardness can be 
reduced to any particular standard by placing them upon a 
hot bar or plate of iron, or upon the surface of melted lead, 
or in a bath of a more fusible metal kept at a certain heat, 
or in hot sand or burning charcoal ; or the articles may be 
held in the inside of an iron ring heated to redness, or they 
may be placed in the mouth of a furnace, or in an oven 
heated to the proper temperature, or they may be placed in 
or upon a gas stove specially constructed, or they may be 
heated in any other convenient way. 

The above methods of applying the heat for tempering 
are to suit those kinds of articles which have been wholly 
(|uenched. When any of the above methods of applying 



70 The Treatment of Steel 

the heat is adopted, and the articles are exposed to a higher 
degree of heat than that which is required to reduce them 
to the exact temper, they must be removed from the heat 
immediately they attain the desired color, otherwise the 
temper will become too far reduced, or in other words the 
articles will be too soft for the purpose they are intended 
for. After they are removed from the heat they may be 
immersed in water or oil, or they may be allowed to cool in 
the air of their own accord ; for it matters not w^hich way 
they become cold, providing the heat has not been too sud- 
denly applied ; for when the articles are removed from the 
heat they cannot become more heated, consequently the 
temper cannot become more reduced. But those kinds of 
tools which are heated further than what they are required 
hard, such as a large portion of the small kinds of turning 
tools, cold chisels, and the larger kinds of drills, and num- 
bers of other kinds of tools, and which are only partially 
dipped, and which are afterward tempered by the heat 
from the back of the tool, must be cooled in the water the 
moment the cutting part attains the desired color, otherwise 
the body of the tool will continue to supply heat, and the 
cutting part will become too soft. 

It is, perhaps, too obvious to require remark, unless it be 
for the information of those who are unaccustomed to these 
processes, that if, after tempering an article, it proves too hard 
for the purpose it is intended for, it is not absolutely necessary 
to reharden it, though in some instances it is more conve- 
nient to do so ; the temper may be further reduced by expos- 
ing it again to heat ; but, if an article is too far reduced in 
temper, it becomes then absolutely necessary to harden it 
over again. When a very large number of small articles are 



Hardening and Tempering Steel 71 

required to be tempered, it will be too slow a process to 
temper them to a certain color ; therefore, a more expedi- 
tious method must be adopted. A very convenient way of 
tempering a large quantity of small articles at once, and of 
heating them uniformly, no matter how irregular their shape, 
providing the heat is not too suddenly applied, is to put 
them into a suitable iron or copper vessel with as much tal- 
low or cold oil as will just cover them, and then to place 
the whole over a small fire and slowly heat the oil until a 
sufficient heat is given to the articles for the temper required. 
It may be well, perhaps, to remind the young mechanic 
that the temperature of the oil or tallow may be raised to 
600 degrees of heat, or rather more ; consequently, any 
temperature below a red heat may be given to the articles 
by the heated oil. Certain degrees of temper retained by 
steel articles when they are heated in oil may be estimated 
by the following circumstances : When the oil or tallow is 
first observed to smoke, it indicates the same temper as that 
called a straw color. The temperature of the oil, if measured 
by the thermometer, will be about 450* degrees. 

If the heat be continued, the smoke becomes more abun- 
dant, and of a darker color ; this indicates a temper equal 
to a brown. The temperature of the oil at this stage, if 
measured by the thermometer, will be about 500 degrees. 
If the oil or tallow be heated so as to yield a black smoke 
and still more abundant, this will denote a purple temper. 
The temperature of the oil at this stage, if measured by the 
thermometer, will be about 530 degrees. The next degree 
of heat may be known by the oil or tallow taking fire if 
a piece of lighted paper be presented to it, but yet not so 

*P"ahrenheit. 



72 The Treatment of Steel 

hot as to burn when the lighted paper is withdrawn. This 
will denote a blue temper. The temperature of the oil 
at this stage, if measured by the thermometer, will be 
about 580 degrees. If the articles are lifted out of the 
vessel at this period, they will be found to possess a con- 
siderable amount of elasticity. This temper is not unfit 
for some kinds of springs, but only when a rather mild 
kind of steel is employed ; the steel in this state may be 
wrought; that is, it may be turned or filed, though with 
difficulty. 

The next degree of heat may be known by the oil or tal- 
low taking fire and continuing to burn, at the same time 
rising higher in the vessel. If the articles are lifted out of 
the vessel at this period, the oil will burn upon them with a 
white flame. This is the temper which is mostly used for 
spiral and some other kinds of springs. 

If the whole of the oil or tallow be allowed to burn 
away before the articles are lifted out of the vessel, it im- 
parts the temper which clock makers mostly use for their 
work. This temper is the lowest used, when the steel is 
required to be at all harder than in its natural state ; for 
a small degree of heat more would just be seen (red) in a 
dark place. 

Any single article, to spare the trouble of heating it in a 
vessel with oil or tallow, may be smeared with oil or tallow 
and held over a clear fire, or over a piece of hot iron ; or, if 
the article is small, it may be held in a gas flame, or in the 
flame of a candle, and its temper, when heated, ascertained 
in a similar manner. It will not, perhaps, be out of place to 
state, that I was once asked by a young man the way to har- 
den and temper spiral springs made of steel wire. I informed 



Hardening and Tempering Steel 73 

him that he must first of all harden them either in water or 
oil, according to the substance of the steel ; and, if he had a 
sufficient quantity to do which would pay for the waste of 
the oil, it would be a very convenient and expeditious method 
to tie them all together with a piece of iron wire, and place 
them in an iron saucepan or any other suitable vessel he 
might chance to have, with as much oil or tallow as would 
cover them, and then to place the whole over a small fire, 
and slowly continue the heat until the oil takes fire, and 
continues to burn ; after which, to lift the springs out of the 
vessel by means of an iron rod, and then to give them one 
dip into some cold oil. This was to give the springs a black 
color ; they were then to be allowed to cool in the air of 
their own accord. 

When I gave the above information, I did not think for 
one moment that this young man would attempt to boil the 
oil over the fire in the dwelling house ; but he informed me 
that he did so, and the result was that he nearly set the 
house on fire. I have just mentioned this circumstance 
merely as a warning to those who are unacquainted with the 
nature of oil at this high temperature, so that they may not 
fall into the same error ; they must not attempt to boil oil 
unless they have a place suitable for it, or serious accidents 
may happen. 

Before putting any article in the fire to heat it for harden- 
ing, it is necessary to examine its shape in order to know 
which way it will require to be immersed in the water so 
as to lessen the risk of its cracking ; every kind of article 
requires to be dipped a particular way according to its 
shape. For instance, if the article is unequally thick and 
thin, or in other words, if there is a stout part and a thin 



y4 The Treatment of Steel 

part, the stoutest part should always enter the water fore- 
most. By dipping the article with the stoutest part of it 
entering the water foremost, it causes the steel to cool more 
uniformly, and lessens the risk of fracture. If the thinnest 
part of the article be allowed to enter the water foremost, it 
increases the risk of fracture, because it will become cool 
much sooner than the stouter part of the article, consequently 
the stout part of the article contracts by the loss of heat 
after the thin part is fixed ; the thin part in its then hard 
and brittle state cannot give, consequently it breaks ; or, if 
it does not break at the time of the hardening of it, it is held 
in such a state of tension (strain) that it is ready to break 
when applied to the work. 

Though it is requisite when hardening steel articles to let 
the stoutest part of the articles enter the water foremost, in 
order to allow the steel to become cool more uniformly, still 
it is not practicable in all instances to get the stoutest part 
of the articles into the water foremost, as will subsequently 
be shown. 

When it is not practicable to get the stoutest part of some 
kinds of articles into the water foremost, some other method 
which will keep the thin part of the articles from cooling too 
suddenly, and which will cause the steel to become more 
uniformly cool, must be resorted to. The various methods to 
be adopted for lessening the risk of fracture when hardening 
various kinds of articles, will be explained as we go along. 

The water which is to be used for hardening steel tools, 
or any other kind of articles made of steel, should never be 
quite cold, but should have, as the term is, the chill taken 
off, or, to use other words, the water requires to be made a 
few degrees warmer. The reason for this is, that when 



Hardening and Tempering Steel 75 

water of too cold a temperature is used, it abstracts the heat 
so suddenly from the surface of the steel that it causes a too 
sudden contraction of the surface steel, and the expansion of 
the interior steel in its still red-hot state is more than the 
hardened crust can bear, consequently it frequently causes 
the steel to break. 

It is quite probable that the interior steel for the moment 
becomes both heated and expanded in a higher degree by 
the sudden compression, for the sudden contraction of the 
surface steel by the sudden loss of heat must act on the 
interior steel something similar to a blow from a heavy ham- 
mer or the pressure of a squeezer ; and if the steel should 
happen to be a little too hot at the time of dipping it into 
pure cold water, there is as much danger of its breaking as 
there is of a glass bottle breaking when boiling water is 
poured into it; heat and cold act on glass and other brittle 
substances in a similar manner that they act on steel. When 
boiling water is poured into a glass bottle, the expansion of 
the inside glass is so sudden that it is more than the outside 
can bear, consequently the bottle breaks ; if the glass is 
heated to a red heat and plunged into cold water, it breaks 
into a quantity of small pieces from the sudden contraction ; 
if a stone is thrown into the fire, it breaks from the sudden 
expansion of its surface. 

The more the water is used for hardening steel the softer 
it becomes, and has a tendency to act less suddenly upon 
the steel ; consequently, the less frequently the water used 
for the purpose is changed the better it is for hardening the 
steel — that is, providing the water has not by continual use 
become greasy. The water is not made better for giving the 
steel a greater degree of hardness by being long in use, but 



76 The Treatment of Steel 

it is made better for the purpose because it is less likely to 
crack the steel than fresh water ; therefore, as the water 
wastes, fresh water should be added t,o it. As it is neces- 
sary to clean the tank out occasionally, it would be well be- 
fore using fresh water to make it quite hot, by putting bars 
of hot iron into it and allowing it to become nearly cold 
again before using it, or the chill may be taken off the water 
and the water made softer by putting some ignited charcoal 
or wood ashes into it. It is obvious that the colder the 
water the more effectually it hardens the steel, and the more 
especially when the steel is immersed suddenly and a rapid 
movement is given to it while it is becoming cool ; but when 
fresh cold water is used there is always greater danger of the 
steel cracking. Brinish liquids, such as aquafortis, urine, or 
water charged with common salt, etc., produce rather more 
hardness than plain water ; but, for most articles, plain water 
with the chill off gives sufficient hardness to the steel. 
Water at about sixty degrees measured by the thermometer 
is the most suitable temperature to prevent steel cracking in 
hardening. Water holding soap in solution prevents the 
steel from hardening. There are certainly ?ome kinds of 
tools, also some pieces of work used in machinery, which 
require to have a greater amount of hardness given to them 
than can be given by plain water ; there are some kinds of 
gauges, burnishers and certain kinds of dies which require 
to be very hard, so that it becomes necessary at times to use 
a saline liquid ; a file requires also to have a nice hard tooth. 
When steel is required to be made extremely hard it may 
be quenched in mercury (the chemists' name for quick- 
silver), but this fluid it is obvious can only be used on a 
small scale. 



Hardening and Tempering Steel 77 

All bright articles which are made of steel, and which 
require to be hardened, are the better for being heated, 
previous to immersion, in contact with carbon. By heating 
steel in contact with carbon, or by supplying a small quantity 
of carbon to the surface of the steel after it is heated, it favors 
the steel in hardening ; but, though it is better to supply a 
small quantity of carbon to the surface of the steel, still it 
is not absolutely necessary to do so, because very satisfac- 
tory results are obtained with some kinds of articles by heat- 
ing them in red-hot lead previous to immersion. When 
red-hot lead is used as a source of heat, the method of sup- 
plying carbon to the surface of the steel cannot conve- 
niently be adopted ; neither can the method of supplying 
carbon to the surface of the steel be conveniently adopted 
when some other methods of heating steel are adopted, such 
as heating some small steel articles between the heated jaws 
of a pair of tongs, or between two heated pieces of bar iron, 
or in a gas flame, the flame of a candle, etc. To supply 
carbon to the surface of steel articles, the articles may be 
inclosed in a sheet-iron case or box, and surrounded on all 
sides with either wood charcoal or animal charcoal ; the 
whole will require to be placed in a furnace or hollow fire 
and heated to redness. Wood charcoal is too familiar to every 
one to require remark in this place ; but it may be necessary 
to state that the animal charcoal here spoken of is nothing 
more than any animal matter — such as horns, hoofs, skins, 
or leather, etc., just sufficiently burnt to admit of being 
reduced to powder. If it is found more convenient to heat 
the articles in the midst of the ignited fuel of an open or 
hollow fire, it is advisable to do so ; but when any bright 
steel article is heated in an open or hollow fire, free of wood 



7 8 The Treatment of Steel 

or animal charcoal, it ought always to be coated with prus- 
siate of potash, or some other substance which will, after it 
has arrived at a red heat, protect it from the direct action 
of the fire and water, at the same time supplying a small 
portion of carbon to the surface of the steel. Though bright 
steel, when heated in the midst of the ignited fuel of a hol- 
low or open fire, is the better for being coated with the prus- 
siate of potash, still there are instances when it will be 
advisable not to use it ; for instance, if the potash were used 
in hardening saws which require to be sharpened with the 
file, it would cause greater difficulty to file them ; conse- 
quently, in such an instance, the potash should not be used. 
When it is required to coat any steel article with the prussi- 
ate of potash, the article will require to be heated to redness 
before the potash is put on to it, otherwise it is useless to 
put it on, for the steel requires to be sufficiently hot to fuse 
the potash when first it is applied for the potash to be of 
any practical service to it. The potash should always be 
finely powdered and placed in a small box, the lid of which 
should be full of small holes, similar to a grater or pepper- 
box. The reason for this is that it is the most economical 
way of using it, especially if the article is held over a piece 
of plate iron whilst the potash is being put on ; what portion 
of the potash falls upon the plate must be returned to the 
box, and thus prevent it being wasted. 

After heating any steel article to redness and sprinkling 
the potash upon it, it must be returned to the fire for a few 
minutes, or until it attains the desired heat ; the article is 
then ready to be immersed in the water. Sometimes when 
the article is very large it is necessary to draw it from the 
fire a second time and sprinkle it again with the potash, in 



Hardening and Tempering Steel 79 

order to give it a thicker coat before it is immersed in the 
water. 

Steel which is hardened with the skin upon it, will un- 
doubtedly be the better if it be sprinkled with the prus- 
siate of potash ; for it has always a tendency to penetrate 
through the thin oxide, and supply carbon to the surface of 
the steel, which, perhaps there is no necessity for repeating, 
is favorable to the steel in hardening. 

It may be well to state that the access of air to the potash 
should always be prevented, when the potash is not in use. 

Steel in the state it leaves the forge, with the skin or thin 
scale upon it, is less liable to break in hardening than steel 
which is brightened previous to hardening. The skin or 
thin scale upon the steel prevents the water from acting too 
suddenly upon the steel ; consequently the contraction is 
slower. Common turning tools will always stand better ; 
that is, they will keep a finer and firmer edge, if they are 
hardened with the skin upon them, than they will if they 
were brightened (either by filing or grinding) previous to 
hardening ; in fact, all tools that can be ground and sharp- 
ened upon the grinding stone after they are hardened, will 
be the better for being hardened with the skin upon the 
steel ; and, if properly forged by the tool smith (who is gen- 
erally as well acquainted with the proper shape of tools as 
the mechanic who uses them), the tools will require very 
little grinding ; and as for water cracks in the steel, there 
will be none. When turning tools are made of the best cast- 
steel; and hardened previous to the removal of the skin or 
scale, and which are not intended to have very keen edges 
but which are intended to sustain a good hard edge for cut- 
ting iron and other metals (cast-iron especially), they will 



8o The Treatment of Steel 

not require to be tempered after being made hard, but 
the heat should be carefully regulated at first, as the 
most useful hardness is produced by that degree of heat 
which is just sufficient to effect the purpose ; for it is quite 
reasonable to suppose that the hardness of steel depends 
upon the crystallization, and the intimate combination of 
its carbon ; therefore, the heat which effects this must be 
the best. 

As there are a number of tools used in the turnery which 
cannot be ground upon the grinding stone, owing to their 
peculiar shapes, it becomes necessary then, while the steel is 
in its soft state, to fit these kinds of tools up with the file, or 
to form them in the lathe, or some other machine ; conse- 
quently these kinds of tools cannot be hardened with the skin 
upon them. But, as there is greater liability of brightened 
steel breaking in hardening than that which is not brightened, 
and as some kinds of tools cannot be ground after they are 
hardened, it becomes an object of importance that they 
should stand well. Therefore, extra precautions must be 
used when hardening these kinds of tools ; for, were their 
cutting edges to chip through being a little too hard, or rub 
off through being a little too soft, they will be practically 
useless for the purpose they are intended for, until they have 
been softened and fitted up again, and subsequently hardened. 
In some instances the tools would be w^hoUy useless ; this 
would be the case with screw taps, and some kinds of 
reamers, broaches, etc., for their original sizes would be lost. 
It must be obvious, then, that if extra care is required with 
some kinds of tools, it must be with those kinds which take 
a great amount of labor and time to make them ; also with 
those kinds which cannot be repaired. 



Hardening and Tempering Steel 8 i 

It is well known that, when iron is heated to a high tem- 
perature, and forged upon the anvil, a thick unequal scale is 
formed upon the surface of the iron, by the action of the 
oxygen of the atmosphere ; and if steel is heated to the same 
degree, and forged upon the anvil, a thick unequal scale is 
formed upon its surface in a similar manner as it is formed 
upon the surface of iron. This thick unequal scale would 
cause the steel to harden unequally, if it were not removed 
previous to hardening of the steel ; but it must be borne in 
mind, that, when tools are made of the best cast-steel, and 
forged at the proper heat, and the anvil kept clean during 
the time they are forged, it will prevent this thick unequal 
scale being formed ; but a very thin equal skin or scale will 
be formed. This thin equal scale does not prevent the steel 
hardening equally, neither does it prevent the steel becom- 
ing sufficiently hard for most purposes ; but it will prevent 
the surface steel becoming cool too suddenly, consequently 
it must be obvious that it will have a tendency to prevent 
the steel breaking in hardening. 

When steel is required to possess the greatest possible 
degree of hardness, it is obvious that the scale must be re- 
moved previous to hardening of it. 

There are many large steel articles broken after harden- 
ing them, by taking them out of the water before they are 
thoroughly cold; and, perhaps, a few words upon this will 
not be out of place. It is the opinion of many mechanics 
that the cause of steel breaking after it is lifted out of the 
water is the action of the air upon the steel, when first the 
steel comes in contact with the air. It is true that large 
masses of steel frequently break immediately the steel is 
lifted out of the water ; but I am at a loss to see in the 



82 The Treatment of Steel 

slightest degree what effect the air can have upon the steel 
in this instance. My opinion is this, and which I have 
formed from experience, that if the steel does not break dur- 
ing the time it is becoming cool, there is no more danger of 
its breaking after it is lifted out of the water than what there 
was of its breaking in the water, that is, providing the steel be 
allowed to remain in the water until its center becomes quite 
cool. During the time the steel is in the water becoming 
cool, and after a certain amount of heat is abstracted from 
the outer crust, there is a peculiar motion or vibration of the 
interior particles in rearranging themselves according to 
their form. This peculiar motion weakens the cohesion of 
the particles. The tension of the steel at this period is in 
one direction ; but let the steel be lifted out of the water 
before the central steel has become quite cool, and the 
tension is reversed in an opposite direction. This is caused 
by the central steel imparting heat to the inner side of the 
hardened crust ; and this sudden change is frequently more 
than the hardened crust can bear, and causes the steel to 
break. If the steel does not break, it is held in such an un- 
equal state of tension, from the particles not being allowed 
sufficient time, before they were again disturbed, to assume 
the exact arrangement to which they are naturally disposed, 
that the tenacity of the steel must more or less be weakened. 
It is not requisite that the steel should lie in the hardening 
tank until the steel and the water become quite cool ; for in 
some instances the steel article is required for immediate use. 
In such instances, any vessel, such as a hand bowl or a water 
bucket, etc., may be sunk into the tank, and the steel arti- 
cle or articles may, while the vessel is under the surface of 
the water, be lifted into the vessel ; after which the vessel 



Hardening and Tempering Steel %i^ 

can be lifted out, with as much water in it as will cover the 
article or articles. The vessel may then be sunk, with the 
article or articles still in it, into another tank of quite cold 
water, or the vessel may be placed under a water tap, and 
cold water run upon the articles ; and when they are quite 
cool they can be lifted out with safety. It will be obvious 
that the greater the mass of steel the greater the risk of its 
breaking by being removed from the water before it is 
thoroughly cold. 

There are many articles cracked in hardening by heating 
them all over, or throughout their body, and then partially 
dipping them into the water. All kinds of articles which 
are heated all over are the better for being dipped and hard- 
ened all over ; and then, if one part of the article is required 
softer than the other parts, it is best to soften it after. To 
spare this trouble, at the same time lessen the risk of frac- 
ture, it will be well not to heat some kinds of articles in any 
other part but that which is required hard, and then to 
entirely quench them. The heat of course must not termi- 
nate upon the article in a strict line, but should be gradually 
tapered off. It is obvious that the heat will not terminate 
in a strict line when the article is heated in a common 
smith's fire ; but, when red-hot lead is used as a source of 
heat, the heat upon the article is liable to terminate in a 
strict line unless a vertical movement be given to the article. 
If only a certain part of a steel article is required to be 
hardened, and the article be heated throughout its body, and 
the water into which the article is to be put be quite cold, 
and the hardener in dipping it stop at any particular part, at 
the same time holding it quietly without giving it a move- 
ment while it is becoming cold, there is always great danger 



84 '^i^'he Treatment of Steel 

of the article cracking at the very spot which is level with 
the surface of the water; and sometimes the article will 
break asunder at the particular spot as evenly as though it 
had been cut with a saw. The tools required by the mill- 
wright, pattern maker, carpenter, joiner, and cabinet maker 
are those kinds of tools which are generally attended with 
the greatest risk by being heated throughout their body, and 
only immersed half their depth into the water ; especially the 
small and middle-sized varieties of the best kinds, which are 
always made wholly of the best cast-steel, and which are 
generally filed or ground bright, and fitted to shape previous 
to hardening. The tools required by these different artists 
do not differ so much from each other in construction and 
name as in size, though the very large tools used by mill- 
wrights, carpenters, and others for heavy, coarse work are 
generally composed of iron and steel welded together, the 
steel forming but a small portion of the whole mass of metal. 
With these kinds of large tools there is less risk of fracture 
in hardening, because it is generally shear steel or a mild 
kind of cast-steel (steel containing a smaller proportion of 
carbon) which is used for welding to the iron. It is obvious 
that if the steel be properly welded to the iron, a flaw will 
be less likely to occur, and a rupture more difficult to start. 
From these statements the reader may, perhaps, be in- 
clined to think that I am condemning the method which is 
so much practiced in the art, that of partially dipping the 
articles and afterward tempering of them by the heat at the 
back of the tool or article ; but it is not my object to con- 
demn a method which I know from experience to be in a 
considerable number of instances very convenient and very 
economical ; but knowing from experience that certain 



Hardening .and Tempering Steel 85 

kinds of articles are so liable to crack when the method of 
partially dipping them is adopted, I have made it my object 
to state the cause of their cracking, and to give such reme- 
dies as will, in a great measure, prevent these water cracks. 
When the method of partially dipping a steel tool or other 
kind of article is adopted, the article may generally be pre- 
vented from cracking by simply putting the water in motion 
previous to dipping the article, or by giving the article a 
quick movement when it is in the water as far as it is re- 
quired hard ; either of these methods will prevent the water 
from acting so evenly in cooling it in a strict line ; either of 
these methods causes the line between the hard and soft part 
of the article to occupy more space, and lessens the risk of 
fracture. Water cracks may also be prevented in that part 
of any article which is required to be level with the surface 
of the water, by simply coiling a piece of binding wire round 
that particular part, and when sufficiently heated, coating it 
with the prussiate of potash previous to immersion. This 
method prevents the water from acting so suddenly or evenly 
upon the steel, at that particular part of the article ; conse- 
quently it prevents its cracking. 

Chipping chisels, drills and all other kinds of tools which 
are only partially dipped into the water, should never be held 
still while they are becoming cold ; but they should, after 
they are dipped to the required depth, have a sudden verti- 
cal or other movement given to them. I have no doubt that 
many have noticed when they have been chipping that their 
chisels have sometimes broken off about an inch or rather 
more from the cutting edge, or at that part of the chisel 
which was level with the surface of the water when it was 
hardening. The cause of the chisels breaking in this par- 



86 The Treatment of Steel 

ticular spot arises in a great number of instances from the 
chisels having been held quietly in the water when harden- 
ing. The water cooling them across in a straight line causes 
the hardened part to tear from the soft part, and the chisels 
sometimes break with a very light blow of the hammer, and 
sometimes with the very first blow. I have myself witnessed 
the ends of drills drop off by simply dabbing their points 
into the wooden bench. I have also witnessed the ends of 
drills drop off at the grinding stone when they were being 
sharpened, after having been repaired. I have also wit- 
nessed the ends of drills drop off on the slightest application 
to the work ; and from no other cause but from the drills 
having been held quietly in the water when hardening. But, 
as these kinds of articles are generally hardened with the 
skin on the steel, they are less liable to break than articles 
which are brightened previous to hardening. I recollect 
once having a quantity of small flat drifts to harden, which 
had triangular grooves cut in them, to form sharp cutting 
edges, something similar to a file, but cut coarser and deeper, 
and I was requested to leave the top part of them (called the 
heads) soft. So I put a certain number of them into an iron 
box and surrounded them on all sides with charcoal dust ; 
luting the box with clay, I placed it in a hollow fire and 
slowly heated the whole to redness, after which I opened the 
box and let the contents drop from the box into the water 
tank, with the intention of subsequently softening the heads. 
After taking them out of the water and examining them, I 
found a number of them very crooked ; this was owing to 
their being so slight and going from the box so suddenly 
into the water. As these kinds of tools are required for 
clearing, truing, and finishing holes, it is obvious that this 



Hardening and Tempering Steel 87 

defect of being crooked is very detrimental, for these tools 
cannot produce true work if they are crooked, besides, they 
are more liable to break when they are struck with the ham- 
mer than if they were straight. 

As the above method did not afford a very satisfactory 
result, I adopted another method. I placed a certain num- 
ber of them in a sheet-iron pan without a lid upon it ; I 
surrounded the drifts with charcoal dust, the same as 
previously, and heated the whole to redness in a hollow fire ; 
as they became heated I gripped separately the head of each 
drift with the pliers, and dipped it endways and perpendicu- 
larly and slowly into the water. This method had the effect 
of causing them to keep straight and answering the purpose 
so far, but it took a longer time to dip them separately ; so 
thinking to save this extra time, I thought I would only dip 
them in the water as far as they were required hard, and 
that would save the time and trouble of softening the parts 
which were not (according to order) to be made hard, 
namely, the heads of the drifts. But not caring about 
going ahead with any large quantity until I made myself 
sure that all was going on well, after I had dipped 
about two dozen of them, I thought it necessary to examine 
them, and I did not find one of them but what was 
cracked at that part of the drift w^hich was level with the 
surface of the water when hardening them ; so I dipped 
the remainder of them all over, and separately, and hard- 
ened them throughout, and not a crack appeared in one 
after. After tempering them to the proper temper, 1 made 
some lead red hot in an iron ladle and dipped the heads 
that were to be soft into it, and accomplished my object 
very nicely. 



88 The Treatment of Steel 

This tearing of the particles from each other when the 
hardening terminates in a strict line is not at all times suffi- 
cient to cause the steel to break asunder, neither is it at all 
times sufficient to show signs of fracture ; but whether the 
steel breaks asunder or not, or whether there are signs of 
fracture or not, this tearing of the particles from each other 
when the hardening terminates in a strict line, must always 
with highly carbonized steel more or less take place, when 
it is known that hardened steel occupies more space than 
soft steel, and that the density of the steel is different in the 
two states. 

When it is required to harden large circular cutters which 
have teeth round their circumference, or large cutters hav- 
ing teeth on their sides as well as on their circumference, or, 
I may state, such cutters as those which have previously 
been treated of, they may be enclosed in a sheet-iron case 
or box and surrounded on all sides with either wood char- 
coal or animal charcoal. The box will require to be luted 
with clay or loam, and the whole placed in a furnace or hol- 
low fire and heated to redness. A certain amount of time 
is essential to allow the steel to soak, or, in other words, to 
get heated uniformly throughout. After the cutters are 
properly heated they must be lifted out of the box sepa- 
rately, not by the tongs or pliers, as they are apt to spoil the 
sharp cutting edges of the cutter, but by a rod of iron (the 
poker) put through the spindle hole of the cutter. The 
hardener must be provided with a proper tool for bearing 
the cutters while he dips them into the water, as the pliers 
do not answer well for this purpose. The most suitable tool 
for dipping the cutters is made by taking three pieces of 
round iron about ^ of an inch in diameter and 3 or 4 



Hardening and Tempering Steel 89 

inches in length. Grip the three pieces at the end with the 
tongs and weld the three opposite ends together, after 
which the welded end must be scarfed and welded to the 
end of another piece of iron, about }^ of an inch in diameter 
and about 18 inches in length ; this forms a stem with three 
prongs at one end of it. The three prongs must be turned 
back so as to stand at right angles with the stem : so 
that when the stem is put through the spindle hole of the 
cutter and gripped with the hand, the cutter will lie upon 
the three prongs. A kind of ring or loop should be turned 
at the end of the stem to keep the stem from slipping 
through the hand by the weight of the cutter, but the loop 
must be sufficiently small to pass through the spindle hole 
of the cutter. 

It may be inquired, will not a long bolt, with a large flat 
head, answer the same purpose as a stem with three prongs 
at the end of it ? The answer to this is : it would answer 
quite as well as regards the bearing of the cutter, but the large 
fiat head would prevent the water from passing freely through 
the spindle hole of the cutter, and would thus prevent the 
cutter from cooling uniformly. After the cutter is lifted out 
of the box, this wire stem must be put through the spindle 
hole of the cutter and gripped with the hand ; and while the 
cutter rests upon the three prongs it must be immersed into 
the water, and instead of moving the cutter backward and 
forward in the tank, it should be moved up and down so that 
fresh water is continually passing through the spindle hole 
during the time the cutter is becoming cool. The deeper 
the tank the better it is for the purpose. Care must be 
taken while moving the cutter up not to allow it to come 
above the surface of the water, or it will be liable to crack. 



90 The Treatment of Steel 

Should the tank not be sufficiently deep to allow moving the 
cutter up and down, the cutter may, after it is beneath the 
surface of the water, be turned sideways, and while one end 
of the wire stem is gripped with the right hand the opposite 
end can be gripped with the left hand. The cutter can 
easily, while it is beneath the surface of the water, be shifted 
toward the middle of the wire stem, which will keep the cut- 
ter or the heated water as it passes through the spindle hole 
of the cutter from burning the hands. It is advisable to keep 
the cutter moving until it is sufficiently cool to be gripped 
with the hand. If more than one cutter has been heated, 
the wire stem must be taken out of the water, as it will be 
required for dipping the other cutters. There is no neces- 
sity for removing the first cutter from the water until all the 
cutters that have been heated have been immersed ; but, if 
the first cutter has increased the temperature of the water 
too high, more cold water should be added to it before the 
second cutter is immersed, and so forth, if necessary, until 
all that have been heated have been immersed. The cutters 
may, after they are hardened, either be allowed to remain in 
the water until the water is thoroughly cold, or they may be 
lifted out of the water by the method previously explained. 
If the cutters are uniformly heated and immersed in the 
water, in the manner just described, they will keep their 
proper shape better than by any other means ; while they are 
much less liable to crack, because they cool more uniformly. 
Any size cutters, dies, bushes, rings, or collars, or ring 
gauges, may be heated and immersed in the water in the same 
manner as circular cutters. It will be obvious that gauges 
or dies which have no holes, or which have only a small hole 
through them, cannot be dipped with the same kind of tool 



Hardening and Tempering Steel 91 

as circular cutters, consequently the pliers will be quite suit- 
able for gripping these kinds of articles. It is not absolutely 
necessary that circular cutters, dies, bushes, rings, gauges, 
etc., should be enclosed in a box to heat them, neither is it 
absolutely necessary to surround them on all sides with wood 
or animal charcoal, as it will answer equally as well, and be 
a far more expeditious method, to carefully and slowly heat 
them in the midst of the fuel of a hollow fire ; but when 
these kinds of articles are heated for hardening in the midst 
of the fuel of a hollow fire, they should always be coated 
with the prussiate of potash. Dies having engraved surfaces 
are undoubtedly the better for being heated in a box and 
surrounded with wood or animal charcoal ; because it would 
not answer very well to fill the fine engraving with the prus- 
siate of potash, neither would it answer to heat them in 
contact with the air. The method of enclosing these kinds 
of articles in an iron box, and surrounding them on all sides 
with wood or animal charcoal, answers three good purposes : 
it causes the heat to be very slowly and equally applied ; the 
surfaces of the dies are rendered rather more steely by the 
absorption of carbon, and it prevents the scaling occasioned 
by the contact of the air. If the dies or any other kind of 
steel articles be previously polished, and well defended from 
the air, they wall be, when hardened, nearly as clean as 
before. Small cutters, after they are hardened, require to be 
brightened in one, two, or more places, and tempered to a 
yellowish wdiite or light straw color. A very good way of 
applying the heat for tempering most kinds of circular 
cutters is to place the cutter upon a piece of round bar iron. 
The most suitable piece of iron for the purpose is made by 
slightly tapering several inches of a piece of round bar iron. 



92 The Treatynent of Steel 

The size of the iron, previous to drawing the taper upon it, 
should be a little larger in diameter than the diameter of the 
spindle hole of the cutter ; so that, if it is necessary (while 
tempering the cutter) to draw the cutter upon the stouter 
part of the iron, so that the iron may fit the hole tightly and 
supply more heat, it may be done. To temper the cutters 
by the use of this piece of iron, the tapered end of the iron 
will require to be heated to redness ; it must then be put 
into the spindle hole of the cutter, the iron and the cutter 
must be supported with the left hand, while a slow rotary 
motion is given to the cutter, by the use of a small stick of 
wood, with the right hand. This method will equalize the 
heat, and cause the temper to be more uniform. As soon 
as the light straw color appears upon the brightened parts of 
the cutter, it must be removed from the heat ; after which it 
may be immersed either in water or oil, or it may be allowed 
to become cool in the air, for it matters not (after it is 
removed from the heat) which way it becomes cool — that 
is, providing the heat has not been too suddenly applied. 
Though this is the most suitable method for applying the 
heat for tempering most kinds of circular cutters, still there 
are some kinds of circular cutters requiring to be tempered 
after they are hardened, where it will be found more conve- 
nient to temper them upon a piece of flat bar iron, heated to 
redness. The heat must not, in any instance, be too sud- 
denly applied. It is advisable, in some instances, when tem- 
pering some kinds of circular cutters upon a piece of flat 
bar iron, to place a piece of cold plate iron between the 
cutters and the red-hot bar, in order that the heat may be 
more slowly and equally applied. It will be found necessary, 
when tempering some kinds of circular cutters upon a piece 



Hardening and Tempering Steel 9;^ 

of flat bar iron, to turn them over occasionally during the 
time they are becoming heated, so as to expose their oppo- 
site sides to the heat, and thus impart to the cutter a more 
uniform temper. The yellowish white or light straw color 
gives tenacity to the steel without materially reducing its 
hardness ; it also lessens the risk of small cutters breaking 
when in use. There is no necessity for tempering or reducing 
the hardness of the largest size circular cutters ; because, 
owing to the larger body of steel, they are much longer 
than the smaller size cutters in becoming cool. A larger 
quantity of steam is also formed at the sides of the large 
cutters, which prevents the water, for a few moments, from 
acting upon the steel ; consequently, the largest size cutters 
cannot become so hard and brittle as the smaller size cut- 
ters. The hardness, of course, depends, in some measure, 
upon the quality of the steel ; likewise the temperature of 
the water and the temperature of the cutters when they are 
immersed in the water. If the quality of the steel, from 
which large and small cutters are made, be equal, and if the 
temperature of the water in which the large and small cut- 
ters are immersed be equal also, and if the large and small 
cutters be equal in temperature when they are immersed, 
this variation in the hardness of the largest and smallest size 
circular cutters, for the reasons just given, must certainly 
take place. It will be obvious, then, that if the smallest size 
cutters require only to be reduced in temper to a yellowish 
white or light straw color, that the largest size cutters 
will not, after hardening, require to be tempered ; but the 
hardening strain may be made more uniform throughout 
the body of large cutters by boiling them in water for several 
hours. 



94 The Treatment of Steel 

Dies which have engraved surfaces, after they are hard- 
ened, require to be tempered ; not because the engraved 
surfaces of the dies are too hard, but because the whole 
body of the steel requires to be toughened, in order to better 
fit the dies to withstand the continual hardship to which 
they are generally exposed when in use. To temper these 
kinds of articles the engraved surface of the dies will re- 
quire to be brightened ; the dies must then be placed upon 
a piece of flat bar iron, several inches of which must be 
heated to redness. If it is required to temper a quantity, 
several may be placed at once upon the bar. Care must be 
taken that all the dies may not arrive at Ihe proper temper 
at the same moment. The dies should not be placed upon 
the hottest part of the bar at first ; but they should, as they 
become gradually heated, be pushed upon the hotter part of 
the bar. The dies will require to be moved occasionally 
during the time they are becoming heated in order to equal- 
ize the heat. As soon as a light straw color appears upon 
the brightened surface of the dies, they must be removed 
from the hot iron ; and, if the heat has not been too sud- 
denly applied to them, they may be allowed to cool in the 
air of their own accord. If the heat has been too suddenly 
applied, and has changed the under side of the die or dies 
to a deep blue color, it will then be requisite to cool them 
either in water or oil, otherwise the bottom side of the die, 
after it is removed from the hot iron, will continue to 
supply heat to the engraved surface and reduce the hard- 
ness too much ; and the die or dies will be practically 
useless for the purpose they are intended for, until the 
operations of hardening and tempering of them have been 
repeated. 



Hardening and Tempering Steel 95 

Hardening these kinds of articles a second time without 
hammering them increases the risk of their breaking ; and 
as they cannot be hammered without spoiling the engraving, 
it must be obvious that very great care is required when 
hardening and tempering them, and the hardener ought 
never to place more of the dies upon the hot bar than what 
he can conveniently manage. 

When it is required to harden steel rings or collars which 
have one thick edge and one thin edge, such as the collars 
of some turning lathes, these may be enclosed, several at 
once, in a sheet-iron case or box, and surrounded on all 
sides with either wood or animal charcoal. The box will 
require to be luted with clay or loam, after which the whole 
may be placed in a furnace or hollow fire, and the steel 
rings or collars heated to the proper temperature suitable 
for hardening them. To spare the trouble of enclosing 
these kinds of articles in a box and surrounding them with 
charcoal, they may be heated in a suitable furnace without 
being enclosed in a box, or they may be heated in the midst 
of the fuel of a hollow fire. When these kinds of articles 
are heated in a furnace or hollow fire in contact with air, 
and the fire free of wood or animal charcoal, they should 
always be coated, previous to immersion, with the prussiate 
of potash, in the manner previously explained. When the 
rings or collars arrive at the proper temperature suitable 
for hardening them, they must be drawn from the fire and 
placed upon the same or a similar kind of wire tool as that 
which is used for bearing circular cutters, while they are 
becoming cool when they are immersed in the water. The 
rings or collars may be immersed in the water separately, 
or two or three may be immersed at once, by taking care to 



96 The Treatment of Steel 

place them upon the wire in such a position that the stoutest 
edge of each ring or collar may enter the water foremost. 
Previous to immersing these kinds of articles in the water, 
and when it is intended to place two or three of them at 
once upon the wdre to be immersed together, it will be 
necessary to examine the depth of the water in the hardening 
tank, in order to ascertain whether the depth of the water is 
sufficient to allow the rings or collars when immersed being 
moved up and down without risk of bringing a part of the 
uppermost collar above the surface of the water. If the 
water is not sufficiently deep to allow these kinds of articles, 
when two or three are immersed together, being moved 
sufficiently to remove the heated water from the inside of 
them, it will be far better to immerse them separately, and 
thus lessen the risk of their breaking. These kinds of 
articles require to be very slow^ly and uniformly heated, and 
should not be plunged too suddenly into the water. The 
more uniform the temperature the less liable are they to 
become oval or out of shape, and the more uniform they 
become cool the less liable they are to crack ; consequently, 
it must readily be seen that these kinds of articles require 
to be immersed very slowly. It must also readily be seen 
that it is quite requisite that the thickest edge should enter 
the water foremost. The degree of heat required to harden 
these kinds of articles will, of course, depend upon the 
quality of the steel from which they are made. Sometimes 
rings and collars are made of the best cast-steel ; they are 
made by punching a long hole near the end of a steel bar ; 
after the hole is punched a round taper mandrel is driven 
into it to widen the hole ; it is then cut off the bar near to 
the hole and worked upon the beak iron of the anvil. When 



Hardening and Tempering Steel 97 

the ring or collar has nearly reached the proper form and 
size it is finished upon a larger mandrel than the first, after 
which it is annealed and turned in the turning lathe to the 
required dimensions. When rings or collars are made of 
the best cast-steel by the method here explained, they will 
only require to be heated to a low red heat to harden 
them. 

Sometimes rings and collars are made of shear steel. 
They are made by scarfing the extreme end of a bar of shear 
steel ; the ring or collar is then partly formed by bending 
the scarfed end of the bar round the beak iron of the anvil ; 
the partly formed ring is then cut off the bar, and the second 
end is scarfed ; the two ends are then brought together, and 
united by welding. The shear steel rings are then finished 
upon a mandrel ; after which, they are annealed and turned 
in the lathe to the required dimensions. When rings or 
collars are made of shear steel by the method here explained, 
they will require to be heated to a bright cherry-red heat to 
harden them. Sometimes rings and collars are made of 
iron, and made to take the place of steel; they are made in 
a similar manner as the shear steel rings or collars. In 
order that the iron rings or collars may be made hard, and 
take the place of steel, they are, after they are finished 
being turned in the lathe with the exception of polishing, 
case hardened. 

It is seldom necessary to temper or reduce the hardness 
of steel bushes, rings, or collars, because the generality of 
these kinds of articles are required for bearings for dift^erent 
parts of machinery, where they have to endure a great 
amount of friction ; consequently they require to be very 
hard to keep them from wearing. Ring and plug gauges, 



98 The Treatment of Steel 

which are made of steel, require a great amount of hardness 
given to them to prevent them from wearing ; consequently 
these kinds of articles will not, after hardening, require to 
be tempered. 

Ring and plug gauges are sometimes made of iron, and 
made to take the place of steel by being case hardened, 
previous to lapping or grinding to their proper sizes. The 
method of case hardening will be explained in a subsequent 
chapter. 

It has already been shown that the more uniformly steel 
articles become cool when hardening, the less liable are they 
to fracture ; and it has been previously recommended that 
the stoutest part of steel articles should enter the water 
foremost. It becomes necessary, perhaps, to state here, that 
this method of immersing steel articles cannot in all instances 
be adopted ; for there are no means by which the stoutest 
part of some kinds of articles can be made to enter the water 
foremost. For instance, with such an article as a feather- 
edge circular cutter it is not practicable to get the stoutest 
part into the water first ; consequently, when this method 
cannot be adopted, some other which will have a tendency 
to cause the steel to cool uniformly must be resorted to. It 
will be obvious that the method of fitting a piece of flat iron 
to the thinnest part of this kind of article cannot conve- 
niently be adopted. The process of concaving the sides to 
reduce the substance of the steel in that part of the cutter 
which is the last to become cool cannot be adopted, because 
this would unfit a feather-edge cutter for the purpose for 
which it is intended. It is evident then, that if none of 
these methods can be adopted with a feather-edge circular 
cutter that there is great risk of the largest kinds breaking 



Hardening and Tempering Steel 99 

from unequal cooling. When it is required to harden a 
large feather-edge circular cutter, it must be very slowly and 
uniformly heated to a cherry-red heat ; the most convenient 
way of heating it is in the midst of the fuel of a hollow fire. 
As soon as the temperature of the cutter is sufficient to fuse 
the prussiate of potash, it must be taken out of the fire and 
coated with the potash, and then be returned to the fire for 
a few minutes, or until it acquires a cherry-red heat ; after 
which it must be drawn out of the fire, and immersed in the 
water in a similar manner as other kinds of circular cutters. 
It will be obvious, from previous remarks, that if the temper- 
ature of these kinds of large cutters be properly regulated 
at first, they will not, after hardening, require to be tem- 
pered. 

Previous to putting this kind of cutter into the fire, it wdll 
be well to cut out two rings from a piece of wire cloth, and 
bind one of them upon each side and at the thin part of the 
cutter. Several short pieces of binding wire w'ill be required 
for binding the wire rings upon the cutter. These wire rings 
will not prevent the thin part of the cutter from hardening, 
but if they be properly bound upon the cutter they will have 
a tendency to cause the potash to cling more firmly to it, and 
prevent the water from acting too suddenly upon the thin 
part of the cutter, thereby causing it to cool more uniformly. 
It will not be necessary to bestow this trouble upon the 
smaller size cutters of a similar shape ; but, with large, ex- 
pensive cutters, to lessen the risk of fracture is not labor 
lost. 

It occurs to me, also, that the use of the wire rings may 
be dispensed with by taking a certain portion of the prus- 
siate of potash and mixing with it a certain portion of flour 



TOO The Treatment of Steel 

or bean meal, or some similar substance, and, after heating 
the cutter to redness, and giving it one coat with the pure 
prussiate of potash, to give the thin part of the cutter a sec- 
ond coat with the mixture. If this mixture adheres to the 
thin part of the cutter it will prevent the water cooling it too 
suddenly, and thus prevent the cutter breaking; but I have 
never given the mixture a trial myself, and cannot speak 
upon its value with certainty. 

When it is required to harden an eccentric ring or collar, 
it may be heated in the midst of the ignited fuel of a hollow 
fire. If it is made of the best cast-steel it will require to be 
uniformly heated to a cherry-red heat and coated with the 
prussiate of potash in a similar manner as other articles, 
after which it must be immersed endways and perpendicu- 
larly in the water and entirely quenched. It will be obvi- 
ous that there would be no difficulty in getting the stoutest 
part of such an article into the water foremost, but it will 
not answer to adopt this method in such a case. If the 
stoutest part were to enter the water foremost it would cer- 
tainly cause the collar to cool more uniformly, and probably 
it would prevent the thinnest side of the collar breaking; 
but then, by going sideways into the water, it would cause 
the hole in the collar to become oval, and the outside of the 
collar to lose its proper shape, which would unfit it for the 
purpose for which it was intended ; consequently it is quite 
requisite that a piece of iron should be fitted to the thin side 
of the collar (as has previously been remarked), and that the 
collar should be immersed endways and perpendicularly in 
the water. 

When it is required to harden a large piece of round cast- 
steel in which a hole has been bored through it (such a 



Hardentfig and Tempering Steel i o i 

piece as has previously been spoken of), it may be sur- 
rounded with wood or animal charcoal in a sheet-iron box 
and heated either in a furnace or a hollow fire in a similar 
manner as other articles, or it may be heated in the midst of 
the ignited fuel of a hollow fire. If it is heated in the midst 
of the ignited fuel, it will require to be coated with the prus- 
siate of potash. Whichever method be adopted for heating 
it, it will require to be heated to a cherry-red heat, after 
which it must be withdrawn from the fire and placed upon 
the same kind of tool as that which is used for dipping cir- 
cular cutters—it must be immersed endways and perpendic- 
ularly in the water. During the time it is becoming cool it 
must be moved up and down in the water in order to allow 
fresh water to pass through the hole, or, in other words, to 
remove the heated water out of the hole ; or it may, after it 
is beneath the surface of the water, be turned upon its side 
and drawn backward and forward until it is cool. 

It may be inquired. What makes the difference whether 
the steel be moved about in the water during the time it is 
becoming cool, or whether it be held still, when it is known 
that heated water always rises to the surface ? The answer 
to this is, that the heated water does not rise to the surface 
so suddenly as the heat is required to be extracted from the 
inside of the article ; consequently it is quite requisite that 
it should be moved about in the water in order that the 
cooler portions of the water may pass through the hole and 
cool the article more uniformly. 

It has previously been stated that it is injurious to bore 
holes too near to the outside edges of steel articles ; but it is 
obvious that boring holes near to the edges cannot, with 
some kinds of articles, be avoided ; therefore, if the hardener 



I02 The Treatment of Steel 

is required to harden any kind of steel article which has 
holes in it near to the edges, it is advisable before putting the 
article in the fire to stop the holes with a piece of loam ; 
this method will prevent the steel breaking at the holes. It 
may be useful to some who are not much accustomed to 
harden steel to know that if a piece of binding wire be 
wrapped round any part of a steel article, and a piece of 
loam wrapped round the wire, it will prevent the steel from 
hardening in that part when it is immersed in the water; 
consequently it will prevent the steel breaking at the part 
where the loam is on. The wire is for no other purpose but 
to prevent the loam from falling off ; the loam requires 
to be dried upon the article before it is put into the fire, 
otherwise it will probably crack and let the water get at the 
steel. But for the sake of making this subject properly 
understood, as it may often prove very useful to the hard- 
ener, let us suppose that the middle part of a piece of one 
inch square cast-steel is required to be hardened and the 
two ends required to be kept soft. We will suppose 
it to be 4 inches in length, and at each end of it a 
countersunk round hole, for the reception of a bolt ^ 
of an inch in diameter, having a cheese - shaped head 
3/^ of an inch in thickness, and ^ of an inch in 
diameter. 

It must easily be seen, by the shape of this kind of arti- 
cle, that if a proper method is not adopted there will be 
some difficulty in hardening it to make it answer the require- 
ment, namely, quite hard in the middle and soft at the ends, 
and not cracked at the holes. If this kind of article could 
be made hot in the middle without heating the two ends 
there would be an end to the difficulty ; but it is obvious 



Hardening and Tempering Steel T03 

that, owing to the shortness of this kind of article, this can- 
not be done, so that, whatever method be adopted in heating 
it for hardening, it will require to be heated throughout its 
body. Fires are sometimes made so that a very short heat 
may be got upon any part of some kinds of articles ; but this 
is an article which will require a certain amount of time to 
soak, consequently the middle part of it cannot be properly 
heated in a short open fire without the two ends becoming 
hot ; it is evident, then, that the article must be heated 
throughout its body. There are various methods that could 
be adopted in hardening this kind of article. First, it may 
be heated in an iron box in contact with charcoal, or it may 
be heated in the midst of the ignited fuel of a hollow fire ; 
when it is sufficiently heated it may be lifted out of the fire 
with the pliers ; one end of it must then be dipped into the 
water and partially cooled, after which the opposite end 
must be dipped and partially cooled in a similar manner. 
This operation is to partly cool the steel to keep it from 
hardening at the parts which are required soft. 

When the temperature of the two ends is reduced beyond 
that which will harden the steel, the whole of the article 
must be immersed in the water and entirely quenched. A 
certain amount of dexterity is required in cooling the ends, 
otherwise the middle part of the article which is required 
hard will become too low in temperature to harden properly. 
By adopting this method, the middle part of the article is 
hardened and the ends remain soft. Still this method is not 
perfect ; because the article frequently becomes cracked at 
the holes when cooling the ends. 

Another method of hardening this kind of article is to 
heat it the same as before, and immerse it at once in the 



I04 The Treatment of Steel 

water. This, of course, hardens the ends as well as the 
middle. The ends may subsequently be softened, though 
very imperfectly, by placing them between pieces of iron 
heated to whiteness ; or, the heat may be more suddenly 
applied by punching a hole (the size and shape of the end 
of the article) in two separate pieces of stout iron, and, 
after heating the two pieces of iron to a whitish heat, plac- 
ing the end^ of the article into the holes. This method of 
hardening this kind of article is not perfect ; because the 
article is liable to become cracked at the holes in hardening, 
and the hardness is liable to become reduced in the middle 
of the articles by heating the ends to get them soft. 

Another method is to heat the article in a hollow fire and 
harden it throughout, after which the two ends may be 
made soft by dipping them, one at a time, in some red hot 
lead. This method is not perfect, because the article is 
liable to become cracked at the holes in hardening, and too 
much time is required for heating the lead for softening the 
ends ; and, as time is money, this becomes a very expensive 
way. Though red-hot lead is an excellent thing for heat- 
ing some articles, and would answer quite well for softening 
the ends of this kind, still it is quite unnecessary to make 
use of it in this instance. 

The most convenient and satisfactory method of harden- 
ing this kind of article, is to wTap a piece of binding wire 
about the holes, and then to fill the holes with loam ; at the 
same time cover the ends and the wire with the loam ; this 
will form a small ball of loam at each end of the article : 
the wire is to prevent the loam falling off. After the loam 
is placed upon the ends it will require to be gradually dried 
before it is put into the fire ; after the loam has become dry 



Hardening and Tempering Steel TOi; 

the article may be placed in the midst of the heated fuel of 
a hollow fire ; that part of the article which is not covered 
with the loam will require to be coated with the prussiate of 
potash ; the potash may be put on without drawing the 
article out of the fire, by using a slip of iron, one end of which 
should be the shape of a spoon ; the article will require to 
be heated throughout to a cherry-red heat, after which it 
must be drawn out of the fire and immersed in the water 
and entirely quenched. Those parts of the article which 
are surrounded with the loam, namely, the holes, will remain 
soft and will not crack, because the water cannot penetrate 
through the loam quick enough to harden the steel. I have 
myself had numbers of articles to harden similar in shape 
to the one just described, and by adopting the method of 
stopping up and surrounding the countersunk holes with the 
loam I never knew one to crack ; though I have seen num- 
bers of the same kind of articles cracked at the holes when 
the loam has not been used. It may be imagined, perhaps, 
that if one method were given for hardening this kind of 
article it would have been sufficient ; but I have thought it 
necessary to mention various methods (at the same time I 
have stated which is the best method) in order that it may 
set the young mechanic thinking, and to afford him a bet- 
ter opportunity of judging for himself which is the best 
method. 

It has previously been stated that sharp internal angles 
are unfavorable to articles which require to be hardened, 
and it has been hinted that sharp internal angles should be 
avoided ; but, as they are required in some kinds of articles, 
and as they are often left in articles when they are not re- 
quired in them, I will state that when I have an article to 



io6 The Treatment of Steel 

harden which has sharp internal angles, I always bind a 
piece of binding wire in the angles of the articles, and 
when I have a circular cutter to harden, which has a flat 
key-way in it with sharp angles, I always make a kind of 
key, by bending a piece of binding wire backward and for- 
ward and then bind it into the key-way of the cutter. This 
of course does not strengthen the cutter, but it has a ten- 
dency to cause the potash to cling more firmly at the key- 
way, and prevents the water acting too suddenly upon the 
weakest part of the cutter. It may, perhaps, be thought by 
some that it will be better to fit an iron key into it ; if an 
iron key were fitted tight into it, it would have a tendency, 
at the period when the cutter was shrinking from the hot to 
the cold state, to split it, as the cutter would have to 
compress the key, which would hold it for the moment in a 
greater state of tension (strain) than if the key were not 
there. 

It has previously been stated that it is injurious to make 
the centers too deep or too large in some kinds of articles 
which require to be hardened ; consequently, it will be well 
to remark here, that, if the hardener meet with articles that 
he considers have too large a center in them, it will be well 
to stop up their centers with a piece of loam previous to 
hardening, and thus prevent them becoming cracked at the 
centers in hardening. 

When it is required to harden a large quantity of small 
or medium-size screw taps at once, they may be enclosed in 
a sheet-iron case or box, and surrounded on all sides with 
either wood charcoal or animal charcoal. Preference should 
be given to the wood charcoal on account of it undergoing 
no change by being exposed to heat, providing the access 



Hardening and Tempering Steel T07 

of air is prevented ; consequently, it can be saved and put 
aside to be used again. The taps will require, of course, 
to be packed in alternate layers, commencing with the 
charcoal on the bottom of the box, to the thickness of 
about ^ of an inch, and finishing with a layer about 
the thickness of the first; the intermediate layers of the 
charcoal need not be more than one-third the thickness of 
the first and last layers. Sufficient space must be left every 
way for the expansion of the steel taps by the heat ; other- 
wise, as they become heated, they will bend and damage 
each other. After the packing is completed and the lid of the 
box put on, it will require to be luted with clay or loam (in 
order to exclude the atmospheric air), after which, the box 
and its contents must be put in a suitable furnace or hollow 
fire, and the whole heated to a cherry-red heat. The fire 
must not be urged, as a certain amount of time is essential 
to allow the contents of the box to be uniformly heated 
throughout. When the whole arrives at the proper heat, 
the box may be drawn to the mouth of the fire, the lid 
removed, and each tap taken out separately and immersed 
endways (screw end foremost) and perpendicularly in the 
water ; or the box may be drawn out of the fire, and the 
whole of the taps immersed at once direct from the box in 
the water. It is obvious that it is a more expeditious way 
of hardening to immerse them all at once. But then they 
are more likely to become crooked than if they were taken 
out of the box separately, and immersed perpendicularly 
and slowly into the water. If the hardening tank is made 
of iron, and the method of immersing the whole of the taps 
at once is adopted, it will be well to sink a piece of board 
to the bottom of the tank for the taps to fall upon ; the 



To8 The Treatment of Steel 

board should be nearly the length and width of the inside 
of the tank, and may be sunk by placing a piece of iron 
upon each end of it. If, in addition to this, a piece of iron 
or a brick be placed at each end, beneath the board, it will 
have a tendency to cause the board to spring, and scatter 
the taps when they are tipped out of the box, which will 
cause them to cool more equally. The taps will, of course, 
require to be packed in such a position that they will, when 
the box is held over the hardening tank, fall endways and 
perpendicularly into the water. When it is required to 
harden a large quantity of the largest size screw taps, they 
may be enclosed in an iron box, and surrounded with car- 
bon in a similar manner as the smaller sizes. They must 
not, like the smaller taps, be allowed to fall direct from the 
box into the water, but must be taken out of the box and 
immersed separately ; but it will be a more expeditious way 
to heat the largest size taps in the midst of the ignited fuel 
of a hollow fire, or a suitable furnace. If this method is 
adopted, the taps will require to be very slowly heated ; but 
several may be heated at once. When they arrive at a 
cherry red heat, which is the heat suitable for hardening 
them, they must be taken out of the fire separately and 
coated with the prussiate of potash, after which they must 
be returned to the fire for a few minutes, or until they regain 
the heat lost while being coated ; after which they must be 
taken out and immersed endways, screw end foremost, and 
perpendicularly in the water. This method of applying the 
heat may also be adopted with small quantities of small or 
middle-size taps. Taps hardened by this method will answer 
the purpose for which they are intended equally as well as if 
thev were heated in a box surrounded with carbon. 



Hardening and Tempering Steel 109 

In all cases the taps must be allowed to remain in ihe 
water until they become quite cool, after which, when taken 
out, and previous to using them, they will require to be tem- 
pered ; but, before tempering, they must be brightened in 
one, two, or more places, in order that the color may be 
seen, and the proper temper ascertained. It will not be 
necessary to brighten the square tops or heads, but only the 
plain round parts of the taps, also one of the concave grooves 
which are cut along the side of the taps. After the taps are 
brightened, they may be tempered by exposing them again 
to heat. When a large quantity is required to be tempered, 
place as many of the taps at once as may be convenient into 
an oven or gas stove specially constructed ; heat the taps 
until a dark straw color appears upon the surface of them. 
This temper is the best that can be given to screw taps which 
are required for general purposes, but those required for a 
special purpose, such as cutting hard cast-iron, or some kinds 
of steel, will then require to be tempered to a yellowish 
white or light straw color. As soon as the proper color 
appears upon the surface of the taps, they must be withdrawn 
from the heat. If the color does not further change after 
the taps are withdrawn from the heat, it is a proof that the 
heat has not been too suddenly applied ; and the taps may 
then be cooled in oil, or they may be allowed to become 
cool in the air of their own accord. Should the color be 
observed to be changing from a straw color to a golden color, 
the taps must instantly be cooled in water ; otherwise they 
will become too soft for the purpose for which they are 
intended. Cooling the taps in oil, after they are tempered 
to the proper color, has a tendency to prevent them rusting 
if they are laid aside. The greater portion of the oil, of 



no The Treatment of Steel 

course, will require to be wiped off ; but the taps need not 
be wiped quite dry. Another method by which screw taps 
may be tempered, is to place a piece of plate iron into and 
near to the mouth of any common furnace, such as those 
which are connected with steam boilers, etc. After the plate 
is placed in the furnace, several of the taps may be placed at 
once upon the plate, and heated until the proper color ap- 
pears. The taps will require to be moved about upon the 
plate during the process in order to equalize the heat. As 
they become heated, and the proper color appears upon 
their surfaces, they must be withdrawn from the heat ; their 
places may be filled up with others, and a continuance of 
the process may be, if necessary, kept up. It is not every 
person who makes screw taps that has large quantities to 
temper at one time, so as to require a furnace, or oven, or 
p:as stove. The amateur mechanic seldom has more than 
two or three sets at most requiring to be tempered at one 
time. There are others who have only a few to temper 
occasionally, merely for the use of the shop ; consequently, 
it will be well to explain another convenient method whereby 
a small quantity of screw taps may be tempered without the 
use of the furnace, oven, or gas stove. A small quantity of 
taps, after they are hardened and brightened, may be tem- 
pered by gripping the top of the taps, one at a time, with a 
pair of tongs, and holding them in the inside of an iron ring, 
heated to redness, until a dark straw color appears upon its 
surface. The heated ring may be placed upon the anvil or 
other suitable place. The screw end of the tap must be 
allowed to project out of the ring when first the heat is 
applied, otherwise the point of the tap, or the leading thread, 
will change its color sooner than the middle part of the tap. 



Hardening and Tempering Steel 



1 1 1 



and temper will be unequal. As the top or plain part of 
the tap changes its color, the screw part must be drawn back 
into the ring. If the jaws of the tongs by which the tap is 
gripped be previously heated to redness, it will be the better, 
as the heated tongs will help to supply heat, and temper the 
taps more uniformly. It will be obvious that if the top or 
plain parts of small screw taps be tempered to a blue, that 
they will be less likely to break when in use ; consequently, 
the heated tongs will be very convenient for tempering the 
plain parts of the taps to a blue at the time that the screw 
part is being tempered to a straw color. The hardener 
ought to be provided with two rings and three pair of tongs, 
so that, while one heated ring and one pair of heated tongs 
are being used, the other ring and another pair of tongs may 
be in the fire becoming heated. The third pair of tongs 
should not be heated, but they should be ready at hand ; so 
that, if it should happen that the heated tongs supplied the 
heat too suddenly to either of the taps, the heated tongs 
could be laid aside for a. few minutes, and the tap gripped 
with the cold pair of tongs. With care, two, and sometimes 
three of the smallest or the middle-size taps may be tem- 
pered without reheating the ring. The larger the diameter 
of the tap, the longer it will be in changing its color, that is, 
providing the heat is properly applied. The thickness of 
the iron from which the ring requires to be made must be in 
proportion to the thickness of the tap ; or, in other words, 
the larger the diameter of the tap the thicker the ring will 
require to be, in order that the ring may retain sufficient 
heat long enough to temper the tap. The diameter of the 
inside of the ring will require to be about 2 inches larger 
than the diameter of the tap. If smaller than this, it will be 



1 1 2 llie Treatment of Steel 

apt to supply the heat too suddenly to the tap. The length 
of the ring will require to be about the same length as the 
tap, except when the ring is required for tempering 
very long tapered taps, such as those sometimes required 
to have the screw part as much as 5, 6, or more inches 
in length. When the ring is required for tempering these 
kinds of taps, it will be more convenient to have it some- 
what shorter than the tap, and move the tap to and fro in 
the ring. 

■ The hardener will find in practice that if two or three 
short rings be heated and placed in a line with each other, 
and made to take the place of a long single ring, it will be 
more convenient for tempering these kinds of taps. 

Screw taps are sometimes required for some purposes as 
much as 18 and more inches in length, the screw part occu- 
pying but a small portion (about 3 inches) of the whole 
length of the taps. When it is required to harden these 
kinds of taps, they may be placed in the midst of the ignited 
fuel of a very small hollow fire; or. they may be placed in the 
inside of a piece of iron pipe, the iron pipe being previously 
placed in the midst of the fuel of an open fire. The screw 
part of these kinds of taps is the only part which requires to 
be hardened ; consequently it is the only part necessary to be 
heated. They must be very slowly and uniformly heated to 
a cherry-red heat, and immersed endways and perpendicularly 
in the water and entirely quenched. These kinds of taps 
will, like the other kinds, require to be brightened and tem- 
pered. The plan of applying the heat by the use of an iron 
ring will be very convenient, but the method of gripping the 
taps with the heated jaws of a pair of tongs, it will be 
obvious, cannot conveniently be adopted; consequently, if 



Hardening and Tempering Steel 113 

they be stout taps, a very thick ring heated to whiteness will 
be required. The whole of the screw part, and about i ^ 
inches of the plain part of the tap, must be allowed to pro- 
ject out of the heated ring, in order that the heat may be 
applied to a certain portion of the plain part of the tap first ; 
otherwise the tap cannot be properly tempered. This part of 
these kinds of taps requires to be in contact with a greater 
amount of heat than will at first sight be readily imagined, 
and it is for this reason that I have suggested a very hot 
ring. If the diameter of the inside of the ring be somewhat 
smaller for these kinds of taps than for other kinds, it will 
not be amiss. As soon as this part of the tap (which is in 
the ring) has changed its color to any of the intermediate 
colors between a light straw and a deep blue, the screw part 
of the tap which is now projecting out of the ring must be 
drawn back into the ring, and tempered to the same color 
as the other kinds of taps, namely, a dark straw color. 

When it is required to harden master taps (commonly 
called by workmen hobs), the same methods adopted with 
other kinds of taps must be applied, with the exception that 
these kinds of taps must be left, in a slight degree, harder 
than the other kinds. The reason for this is, they are 
mostly required for cutting steel, such as the threads of 
screw dies, also for cutting the threads upon those kinds of 
screw tools called chasers, etc. ; consequently the small and 
middle-size master taps will not require to be reduced in 
temper lower than the yellowish white or light straw color. 
It will be obvious from the manner in which master taps are 
grooved, that there is greater liability of their breaking in 
hardening, and less liability of their breaking when in use, 
than the other kinds of taps of the same diameter ; conse- 



114 The Treatment of Steel 

quently, when it is required to harden the largest size master 
taps, the heat should be carefully regulated at first, so that, 
after they are immersed in water, become cool, and taken 
out, they \\\\\ be ready for use, and thus dispense with the 
subsequent process of tempering. The largest size master 
taps will be the better (whether heated surrounded with 
carbon in an iron box, or whether heated in the midst of the 
fuel of a hollow fire) if they are coated with the prussiate of 
potash previous to immersion. 

When it is required to harden large or small screw dies, 
in large or small quantities, they may be heated in a similar 
manner as screw taps, either by inclosing them in an iron 
box and surrounding them with carbon, and placing the 
whole in a furnace, or by placing them in the midst of the 
ignited fuel of a hollow fire. Whichever method is adopted, 
they will require to be uniformly heated to a cherry-red heat. 
They will require to be immersed plain end foremost in the 
water ; or, in other words, the screw part of the dies should 
be uppermost when the dies enter the water. It will be ob- 
vious that, if the dies are immersed separately, there will be 
no difficulty in making the plain end of them enter the water 
foremost ; but in order to approach this method as near as 
practicable, the dies should be packed in the box in such a 
position that they will all have a tendency (when the box is 
opened and held over the water tank) to fall plain end fore- 
most into the water. When the dies are heated in the midst 
of the ignited fuel of a hollow fire, they will require to be 
coated with the prussiate of potash previous to immersion. 
A very convenient box in which to heat a moderate quantity 
of small screw dies or screw taps, may be made by welding 
a plug into the end of a piece of large wrought-iron pipe. 



Hardening and Tempering Steel i i 5 

A loose plug will be required for the opposite end of the 
pipe ; it must be the same size as the bore of the pipe, 
and about i}^ inches in length. Part of the plug must 
be allowed to project out of the pipe for the convenience of 
gripping it with the tongs, or tapping it with the hammer 
when required to be taken out ; otherwise, it may be diffi- 
cult to get it out, especially after it has been luted with 
loam. The plug will require to be temporarily fastened into 
its place; this may be done by boring a hole through the 
pipe and the plug, and driving an iron pin through the two. 
It will be obvious that when a large quantity of screw dies 
or screw taps are required to be heated in a box, the box 
should be larger in proportion to the quantity to be operated 
upon, and the box will require to be made of plate iron. 

After screw dies are hardened, they will require to be 
brightened and tempered. The tempering may be per- 
formed by placing the dies, several at once, upon a hot 
plate of cast metal ; or they may be tempered by placing 
them upon a piece of bar iron, one end of which must be 
heated to redness. Those kinds of dies which are used in 
the screwing machine, and all large screw dies of a similar 
shape, will require to be placed upon the heated iron, screw 
part uppermost, in order that the heat may not be too sud- 
denly applied to the cutting part of the dies. 

As soon as these kinds of dies are observed to be chang- 
ing their color, they must be moved to the cooler part of the 
iron, otherwise the bottom part of the screw part of the dies 
will be apt to become softer than the top part, and the tem- 
per would be unequal. It will sometimes be found neces- 
sary, after the dies are removed to the cooler part of the 
iron, to turn them bottom upward for a few moments, or to 



I 1 6 The Treatment of Steel 

turn them upon their sides, in order to obtain a uniform 
degree of temper. 

Some kinds of screw dies require to be placed upon the 
hottest part of the iron at first, and as they become heated 
should be drawn toward the cooler part of the iron. Other 
kinds of screw dies require to be placed upon the cooler part 
of the iron at first ; and, as they become heated, they re- 
quire to be drawn toward the hotter part of the iron. This, 
of course, depends upon the depth of the dies, or the 
distance between the screw part and the back part of the 
dies. 

The dies must be allowed to remain upon the heated iron 
until their cutting parts become uniformly changed to a dark 
straw color; after which they may be cooled in water or oil, 
or allowed to cool in the air of their own accord, according 
to circumstances previously explained. The smaller size 
screw dies may be uniformly tempered, and the heat very 
gradually applied, by placing them upon a stout piece of 
cold plate iron, and then placing the plate and dies upon a 
thick piece of iron heated to a whitish heat. The dies must 
be turned over occasionally in order to expose all their sides 
to the heat. As their surfaces become changed to a dark 
straw color, they may be pushed off the plate into a vessel 
containing water or oil. If the plate has not become too 
hot, their places may be filled up with others. If the plate 
has become too hot, it may be taken off the hot iron and 
placed upon the anvil face ; it will then in a few^ moments be 
in a fit state for tempering a second quantity. By putting 
the plate back into its place (upon the hot iron) a third, and 
sometimes a fourth quantity, may be tempered without re- 
heatine: the iron. 



Hardening and Tempering Steel 1 1 7 

When it is required to harden a large quantity of those 
kinds of screw tools called chasers, they may be placed (sev- 
eral at once, or as many as may be convenient) in the midst 
of the ignited fuel of an open fire, or they may be placed in 
the midst of the ignited fuel of a very small hollow fire. 
The screw end or cutting part of the chasers requires to be 
heated to a cherry-red heat. The blast, of course, must be 
sparingly used. When they arrive at the proper heat, they 
must be drawn out of the fire ; but, should there be some in 
advance of the others, these must be the first to be drawn 
out, after which the heated end will require to be coated 
with the prussiate of potash. They must then be returned 
to the fire for a few minutes, or until they acquire a cherry- 
red heat, after which they must be immersed in the water 
and entirely quenched. In order to keep up a continuance 
of the process, as they are withdrawn their places in the fire 
must be filled up with others. After the whole of them have 
been immersed and become cool, they will require to be 
brightened and tempered. They may be brightened upon a 
grinding stone or an emery wheel, or by rubbing the top 
surface with a piece of grinding stone, or by an emery stick, 
or a piece of emery cloth. After the chasers are brightened 
they may be placed, several at once, upon a piece of flat bar 
iron heated to redness. The screw end of the chasers must 
be allowed to project some distance (about i^ inches) over 
the heated iron, otherwise the heat will be too suddenly 
applied to the cutting parts of the chasers. As soon as a 
yellowish white or light straw color appears upon the cutting 
parts of the chasers, they must be removed from the heat 
and cooled in water or oil, otherwise the back part of the 
chasers which was in contact with the heated iron will con- 



1 1 8 The Treatment of Steel 

tinue to supply heat, and the chasers will become too soft. 
As the chasers are removed from the hot iron, their places 
can be filled up with others. By having two pieces of iron, 
one piece in the fire becoming heated whilst the other piece 
is being used, a continuance of the process may be kept up. 
After the chasers are taken out of the water or oil, and the 
top surface ground upon the grinding stone, they are ready 
for use. Though this method is a very expeditious one for 
hardening and tempering a large quantity, still it is not 
absolutely necessary to adopt it with a small quantity, or a 
single chaser ; because they may with care be hardened and 
tempered equally as well by heating them and partially 
dipping them into the water and tempering them by the heat 
at the back part of the chaser, without the use of the hot iron. 
It will be obvious that, when this method is adopted, a greater 
portion of the tool will require to be heated, in order that the 
back part of the chaser may retain sufficient heat to temper 
the cutting part after it has been immersed into the water. 

When this method of partially dipping the chaser is 
adopted, it will be advisable to put the water in motion pre- 
vious to dipping the chaser ; or, otherwise, when the cutting 
part of the chaser is beneath the surface of the water, give 
the chaser a quick movement; this will prevent the water 
from cooling the steel in a strict line, and guard against 
water cracks. That part of the chaser which is beneath the 
surface of the water must be allowed to remain in the water 
until it becomes quite cool, after which it must be taken out 
and brightened. In a short time the back part of the chaser 
will supply sufficient heat to the cutting part to temper it to 
the desired color. As soon as the proper color appears, the 
chaser must be entirely quenched ; and, when taken out of 



Hardening and Tempering Steel t i 9 

the water and ground upon the grinding stone, it will be like 
those which have been wholly quenched and subsequently 
tempered on the heated iron, ready for use. 

When it is required to harden a screw plate, it may be 
placed in the midst of the ignited fuel of a very small hollow 
fire, or among the ignited fuel of an open fire. It will re- 
quire to be very slowly and uniformly heated to a cherry-red 
heat; the blast of course must be sparingly used, other- 
wise it will become crooked. There is no necessity for 
heating the whole length of the shank or handle ; but it is 
quite necessary to heat a small portion of it, in order to 
obtain a more uniform heat upon the plate. As soon as the 
temperature of the plate is sufficient to fuse the prussiate of 
potash, it must be withdrawn from the fire, and coated with 
the potash, in a manner similar to other kinds of tools ; after 
which it must be immersed very slowly, endways and per- 
pendicularly, in water. The largest size screw plates will 
generally keep truer by being immersed edgeways and 
horizontally in the water. The screw plate must be allowed 
to remain in the water until it becomes quite cool, after 
which, when taken out, it will require to be brightened and 
tempered. It may be tempered by holding it over a piece 
of flat bar iron (heated to redness) until a dark straw color 
appears upon its surface ; or it may be tempered between 
two pieces of flat iron heated to redness, and placed a certain 
distance apart from each other, in order that the heat may 
not be too suddenly applied ; or it may be held in the inside 
of an iron ring heated to redness ; or it may be tempered in 
a sand bath, provided the temperature of the sand is just 
sufficient to change it to the proper color — if the sand is 
hotter than this, there is a great risk of the threads becoming 



T 20 The Treatment of Steel 

too soft ; or the heat may be applied by any other convenient 
method, after which the plate will be ready for use. 

Screw plates and screw dies are often ruined by being 
used upon iron and steel rough from the forge, and covered 
with scales, which, from their hard, gritty nature, grind away 
the threads. In all. cases the rough scale should be removed 
from the iron or steel, either by the turning tool, file, or 
grinding stone, previous to screwing it with the screw plate 
or the dies. It is not an uncommon practice with some 
workmen, after they have finished forging a piece of iron 
work, and while the iron is at a red heat, to immerse it in 
water and partly cool it, with a view of giving the work a 
cleaner appearance ; but this is a very bad custom, especially 
when the forging requires to be screwed. It very often 
happens that the iron contains veins of steel, which harden 
by immersion ; and, though the metal may not be so hard as 
to prevent its being cut with a hard turning tool, still, when 
it comes to be screwed with the stocks and dies, or with the 
dies belonging to the screwing machine, or with the screw 
plates (which tools are always less hard than the turning 
tools), it will spoil the dies or the screw plates ;■ and because 
this hard place or places do not happen to be detected when 
turning the work (on account of using a very hard tool), the 
steel the dies or screw plate is made of will be thought bad, 
or badly tempered. The fact is, the work should always be 
annealed rather than hardened. In all cases when an impure 
iron is made use of for forgings, and which wall subsequently 
require to be screwed, either with the screw dies or the 
screw plate, or which may require to be cut with circular 
cutters or with circular saws, the forgings should always be 
annealed previous to leaving the smithy. The forgings, of 



Hardening and Tempering Steel i 2 t 

course, will be the better for being annealed supposing they 
are to be screwed with the screw tools belonging to the 
turning lathe ; though it is not of so much importance as 
when they are to be screwed with the dies, or the screw plate, 
or cut with circular cutters, or circular saws, because the 
screw tools belonging to the turning lathe can be ground 
again, provided they chip from being very hard ; w^hereas, 
the generality of screw dies, screw plates, and circular 
cutters, and even circular saws, when very hard, and once 
spoilt, wall not admit of being again sharpened, but will be 
practically useless, until they have been annealed, and cut 
up again, and subsequently hardened. Annealing makes 
the iron more uniform in temper, and will save much 
subsequent trouble ; it will greatly facilitate the work when 
fitting it up. 

When it is required to harden a large quantity of stout 
circular saws at once (for cutting metals), they may be 
enclosed in a sheet-iron case, or box ; they will require to be 
surrounded on all sides with either wood or animal charcoal. 
Sufficient space must, of course, be left every way for the 
expansion of the saws ; otherwise they will become buckled 
in heating. After the saws are enclosed and the box luted 
with clay or loam, the whole may be placed in a suitable 
furnace or hollow fire and the saws heated to a cherry-red 
heat (the fire of course must not be urged). As soon as the 
whole arrive at the proper uniform temperature, the box 
must be drawn toward the mouth of the fire, the lid taken 
off and the saws taken out separately. They may either be 
taken out of the box with the pliers or by a small rod of 
iron, having a small hook turned upon one end of it. The 
saws wall require to be immersed edgeways in a trough 



122 The Treatment of Steel 

containing water, the surface of which must be covered with a 
film of oil. The oil will float of itself upon the surface of 
the water and burn upon the saw as it passes through it. 
The burnt oil forms a coating of coal upon the saw, which 
protects it from the direct action of the water, and lessens 
the risk of fracture. 

Though saws are the better for being enclosed in a box 
and surrounded with charcoal when heating them, still, when 
a single saw is required to be hardened in a hurry, it will be 
more expeditious to place it upon a piece of cold sheet-iron, 
and then to heat the iron and the saw in the midst of the 
ignited fuel of a hollow fire ; and when it arrives at the 
proper temperature, it must be taken off the plate and im- 
mersed in the hardening fiuid. By placing the saw upon a 
piece of cold sheet-iron, it causes the heat to be very slowly 
applied, and it has a tendency to prevent the saw buckling 
in heating. Oil alone, or oil in which tallo\v has been dis- 
solved, is sufficient to give the thinnest kinds of saws a suffi- 
cient degree of hardness ; but those of a medium thickness 
are the better for being hardened in solid tallow (the saws 
may be placed separately between two flat lumps of tallow). 
Tallow differs from oil in the absorption of heat for its 
fusion ; consequently, a more considerable degree of hard- 
ness is given to the steel by the tallow than by the oil ; 
besides, it hardens the steel to a greater depth than oil. 
Very thin blades of steel may be made sufhciently hard for 
some purposes by heating the blades to a red heat and then 
placing them between two heavy surface plates ; the surface 
plates will be better if they be smeared with tallow, previous 
to putting the blade between them. When the saws are 
removed from the hardening trough, they are generally brit- 



Hardening and Tempering Steel 123 

tie and warped ; consequently, they will require to be tem- 
pered and hammered flat. The tempering may be performed 
in a variety of ways, depending of course upon the size, 
shape and quantity. Circular saws, which are required for 
sawing hard substances (such as iron or steel), and which 
have a round spindle hole, . about i inch in diameter, in 
them, will require to be tempered to a light straw color. 
These may be tempered by first brightening their surfaces, 
and then placing them upon a piece of hot iron. The piece 
of iron which will be required for tempering these kinds of 
saws may be made by the following method. Take a piece 
of round bar iron, i inch in diameter and 8 or 9 inches 
in length ; heat one end of it and hammer it so as to 
make it fit into the small square hole in the anvil ; at the 
opposite end of this piece of iron, and at about 2 inches 
from the extreme end, weld a moderate-sized iron collar ; 
the collar should be made of half-round iron, so that it will, 
after it is welded upon the piece of round bar, form a large 
lump, the shape of a round ball. The object of this large 
lump is to retain the heat for a considerable time, so that 
several of the saws may be tempered before the iron will 
require to be reheated. If two of these lumps were made, 
one of them could be in the fire becoming heated, whilst the 
other lump is being used ; so that, if it were necessary, a 
continuance of the process may be kept up. The object of 
having this lump the shape of a round ball is that it may 
not supply the heat too suddenly to the saw. If this lump 
were made flat, it would supply the heat too suddenly, unless 
it were used at a very low temperature ; it is evident it would 
not then temper more than one or two of the saws before it 
would require to be. reheated. The object of having this 



T 24 The Treatment of Steel 

round lump welded upon a piece of round bar is for the 
convenience of keeping the lump in position upon the anvil, 
and to prevent the operator from always being in a stooping 
position when tempering the saws. The iron being finished, 
it is now ready to be heated for tempering the saws. The 
large lump will require to be heated to a red heat, after 
which the opposite end of the iron must be placed in the 
hole in the anvil. The saws may now be placed (one at a 
time) upon the lump; a slow, rotary motion must be given 
to the saw, by the use of a small stick of wood, in order to 
equalize the heat. The end of the round bar at the top of 
the lump will help to supply heat and keep the saw in 
position whilst it is being turned upon the lump. As soon 
as a light straw color appears upon the saw, it must be taken 
off the iron and cooled, either in water or oil ; or, if the heat 
has not been too suddenly applied, the saw may be allowed 
to cool in the air of its own accord. These kinds of small 
circular saws are generally, after hardening, convex on one 
side and concave on the other. This imperfection is owing 
to the outer part of the saw becoming too small to contain 
the central part. When the practice of securing the saws 
upon the spindle by circular plates screwed firmly against 
each side is adopted, a small degree of regular convexity 
is not very detrimental, because the plates bring the 
saw straight; but \\hen they are convex in a greater 
degree, they will require to be slightly hammered. The 
outer part of the saw is the part which requires to be ham- 
mered, in order to expand the outer part and bring the 
middle fiat. 

These kinds of saws may be tempered, and the trouble 
of brightening their surfaces spared, by smearing them with 



Hardening and Tempering Steel \ 1 5 

oil or tallow and holding them one at a time over a slow 
clear fire until the oil or tallow begins to smoke, after which 
the saw must be immersed in oil and partly cooled ; it must 
then be held over the fire the second time, until the oil 
again begins to smoke. If the saw is immersed in the oil 
and held over the fire a third time, it will ensure a more 
regular degree of temper. Care must be taken each time 
the saw is heated not to raise the temperature beyond that 
which is necessary to cause the oil to smoke ; otherwise the 
saw will become too soft for the purpose it is intended for 
— namely, cutting hard substances. By this method the 
saws acquire the same temper as that which they acquire 
when tempered to a straw color. A large quantity of these 
kinds of saws may be tempered more expeditiously by 
threading them upon a piece of iron wire, and then placing 
them in a proper vessel, with as much oil or tallow as will 
cover them (the wire is for convenience in lifting the saws 
out of the vessel), and then to place the whole over a small 
clear fire, or over a gas flame, until the oil or tallow begins 
to smoke, after which the saws must be taken out. They 
may be then cooled in water or oil, or they may be allowed 
to become cool in the air. This indicates the same temper 
as that called a straw color. 

Saw blades which are required for sawing wood require 
to have the greatest amount of elasticity given to them ; 
consequently, after they are hardened, they will require to 
be tempered to the same temper as that called spring tem- 
per. This may be done by exposing the blade, the surface 
of which has been brightened, to the regulated heat of a 
plate of metal till the surface has acquired a blue color ; or 
it may be heated in a sand bath heated to the proper tem- 



126 The Treatment of Steel 

perature. To spare the trouble of brightening them, they 
may, like small circular saws, be smeared with oil or tallow 
and heated over a clear fire. It is obvious that the softer 
the steel is intended to be, the more grease must be burnt 
off ; consequently, those saw blades which are required for 
sawing wood, and which require to be sharpened with the 
file, will require to be heated till thick vapors are emitted 
and burn off with a blaze ; two or three reheatings, and 
partly cooling them in oil, when tempering, will, of course, 
insure a more uniform degree of temper. Saw blades which 
are required for sawing wood, could, like those intended for 
sawing metals, be heated and tempered in hot oil ; but, per- 
haps, it would not be very economical. The oil, of course, 
would require to be heated to a very high degree, in order 
to impart to the saws a spring temper ; so that it is question- 
able whether the time saved by this method would be suffi- 
cient to compensate for the waste of oil, which at this high 
temperature is considerable ; consequently, it becomes those 
who have such things to tempef to adopt those methods 
which will answer their purpose the best. Saw blades, un- 
less hardened in a current of air, are generally, after hard- 
ening, buckled and twisted in various directions ; this is 
caused by an unequal contraction of the blade, and it would 
be almost, it not quite, impossible to prevent this unequal 
contraction, when it may arise from so many causes. The 
metal itself may be unequal in its texture. It may have 
been rolled at a temperature which was not uniform 
throughout the mass, or the blade may have been hammered 
more in one part than another ; this would be sufficient, 
from its unequal density, to cause unequal contraction ; or, 
if the temperature is not uniform throughout the blade when 



Hardening and Tempering Steel 127 

it is immersed in the hardening fluid, it will cause unequal 
contraction. 

Saw blades which have become buckled and twisted in 
hardening, will, after they are tempered, require to be ham- 
mered flat ; this operation requires a considerable amount 
of care and practice. It is obvious that the blades will re- 
quire to be hammered at every part except those which are 
buckled. The hammering draws and expands those parts 
which are not buckled, and removes the unequal tension 
which has been caused by the unequal contraction of the 
blade. The extent to which the blade will require to be 
hammered, of course, can only be ascertained by experience. 

When saw blades are well hammered, and the unequal 
tension has been removed, they are then flat and more uni- 
formly elastic ; but if the crust of the blade be partially or 
wholly removed by grinding, or in any other manner, the 
elasticity is proportionately impaired, and to restore the 
original excellence of this property, the blade will require 
to be again hammered and afterward blued. Saws require 
to be made of the best cast-steel, and, like all other kinds of 
tools, when required for cutting brass, require very sharp 
cutting edges ; they require also to be, in a slight degree, 
harder for brass and cast-iron than for steel or wrought-iron, 
otherwise they soon lose their sharp edges. 

When it is required to harden a single saw, such as is 
used for sawing off the ends of wood screws, or for sawing 
off the ends of small screw bolts, or for occasionally sawing 
the grooves in the heads of screws, it may be heated to a 
cherry-red heat, and then placed flatways and horizontally 
between two lumps of tallow, or it may be pressed edgeways 
into a single lump of tallow. When it is intended to harden 



128 The Treatment of Steel 

the saw by this last method, the saw should be slightly 
hammered at the back previous to heating and hardening 
it, otherwise the cutting edge will, in hardening, become 
convex, and the back edge will become concave. If the 
saw becomes crooked sideways, it may be straightened by 
slightly hammering it with the peen of a small hammer at 
the concave side, at the same time pressing with the 
fingers upon each end of the saw. The saw will be the 
better for being slightly heated previous to hammering it ; 
it may be heated by placing the back side of it upon a 
piece of hot iron. If the saw should be found too hard for 
the purpose it is intended for, the back edge may then be 
placed upon the hot iron, and the saw tempered to a light 
straw color. 

When it is required to harden a lathe center, it may be 
heated in an open fire ; the tapered part only requires to be 
heated, and this only to a low red heat ; the lowest heat that 
it will harden at is the most advantageous, as the center is 
the more likely to keep true, and it will not afterward require 
to be tempered. It must be immersed endways and per- 
pendicularly in the water ; the back end of the center must 
enter the water foremost : it must be allowed to remain in 
the water until it becomes cool, after which it is ready for 
use. Lathe centers for large lathes, on account of the 
heavy weights they sometimes have to carry, ought always 
to be made of the most tenacious cast-steel, which ought 
only to require a low red heat to harden. 

When it is required to harden a large or small quantity 
of fluted or other kinds of reamers, they may be heated in a 
similar manner to screw taps, either by enclosing them in an 
iron box, and surrounding them on all sides with carbon. 



Hardening and Tempering Steel 129 

and placing the whole in a furnace or hollow fire, or by 
placing them in the midst of the ignited fuel of a small 
hollow fire. It will sometimes be more advantageous to heat 
these kinds of articles in red-hot lead, especially when a 
large quantity requires to be operated upon, because this is 
a very expeditious method for heating them, and they gen- 
erally keep truer in heating by being surrounded on all sides 
with the uniform temperature of the lead, consequently they 
will keep truer in hardening. The lead, of course, must be 
heated to a certain temperature suitable to the steel. If the 
reamers are made of the best cast-steel, the temperature of 
the lead need not be raised higher than what is necessary 
to heat the reamers to a cherry-red heat ; if the lead is too 
hot, it will burn the steel, and cause the reamers to be full of 
very small holes, which, of course, will unfit them for the 
purpose for which they are intended. If the lead by chance 
becomes too hot, it may be cooled down to the proper 
temperature by dipping a piece of cold iron into it. 

When it is intended to heat small reamers in red-hot lead, 
it will be necessary (previous to putting them into the lead), 
in order to protect them from the direct action of the heat, 
and to prevent the lead sticking to them, to brush them over 
with a little soft soap ; the largest and middle-size reamers 
will be the better for being brushed over with black lead, 
mixed with water, or they may be brushed over with a mix- 
ture of lampblack and linseed oil. If the black lead and 
water is used, it will be well to dry the reamers previous to 
putting them into the lead, otherwise the dampness may 
cause the lead to fly, and accidents may happen from it. 
Whichever method be adopted for applying the heat to ream- 
ers, they will require to be heated to a cherry-red heat, after 



I JO The Treatment of- Steel 

which they must be immersed separately, endways, perpen- 
dicularly (except half-round reamers), and slowly in the 
water. Half-round reamers are very liable to become crooked, 
or concave on their round side, owing to the round side 
being the last to become cool ; consequently, they will re- 
quire to be immersed in the same steady manner as the 
other kinds, but not so perpendicularly — they will require 
to have a more horizontal inclination. They may be im- 
mersed perpendicularly, provided they are slowly moved 
horizontally in the water in the direction of the round side, 
at the same time that they are being immersed endways. It 
must be borne in mind that red-hot lead will heat the steel 
much quicker than the ignited fuel of the fire ; consequently, 
when large fluted reamers are heated in lead, the cutting ribs 
of the reamers will arrive at the proper temperature much 
sooner than the central parts of the reamers, or before the 
innermost center becomes at all heated ; and if the reamers 
are immersed in the water the moment the cutting ribs be- 
come sufficiently heated (and they may be immersed without 
fear of breaking them), the central parts of the reamers will 
remain soft ; consequently, if large fluted reamers become 
crooked in hardening, they may be easily straightened. 
They may be straightened by laying them upon a block of 
hard wood, or upon a block of lead, and then putting a 
piece of round iron (the size of the groove) into the groove 
at the convex side, and then striking the iron with the ham- 
mer. If the reamers be tempered previous to striking them 
with the hammer, they will straighten the easier. When 
small fluted reamers are heated in red-hot lead, they become 
heated through almost instantly they are put into the lead ; 
consequently, it must be obvious that if these become crooked 



Hardening and Tempering Steel 1 3 i 

in hardenin<(, they cannot be straightened in the same man- 
ner as the larger sizes ; therefore, in order to guard against 
their becoming crooked, they must be allowed to remain in 
the heated lead until they become uniformly heated to their 
innermost center, and then immerse them endways, and 
perpendicularly, and very slowly in the water, and entirely 
quench them ; and if any of them become crooked, it will 
be well to soften them again, then straighten and reharden 
them. Care must of course be taken not to raise the tem- 
l^erature of the lead higher than what is necessary to heat 
the reamers to the proper temperature suitable for hardening 
them. The method I have myself sometimes adopted when 
hardening fluted reamers is this : I have heated them sepa- 
rately in red-hot lead, and then immersed them separately, 
endways, and perpendicularly, in the water, having the water 
of a suitable depth, so that when a reamer was immersed, 
and the extreme end of it made to touch the bottom of the 
tank, and then withdrawn, it would harden the cutting edges 
of the reamer, and leave sufficient heat in the central part, 
so that the reamer would, if it were crooked, admit of 
being straightened, either by placing it between the cen- 
ters of a turning lathe, and striking it upon the convex 
side with a small wooden mallet, or, by placing it upon a 
block of hard wood, or a block of lead, and striking upon 
the convex side with the mallet. As this method requires a 
great amount of experience and dexterity, and as there is 
great risk of the reamers breaking when they are struck with 
the mallet, especially if they be allowed to become too cool 
previous to striking, it will be well, perhaps, for the operator 
(in order to avoid any considerable obstacle) to adopt the 
method previously explained, that of immersing them end- 



T^i The Treatment of Steel 

ways, perpendicularly, and slowly in the water, and entirely 
quenching them. 

Reamers after they are hardened will require to be tem- 
pered, which may be done by adopting similar methods to 
those to be adopted for tempering screw taps. Fluted ream- 
ers will require to be tempered to a yellowish white, or light 
straw color ; six and eight-sided reamers will also require to 
be tempered to a light straw color ; square, and triangular, 
and half-round reamers will require to be tempered to a dark 
straw color. The reason why square, and triangular, and 
half-round reamers require to be reduced lower in temper 
than the other kinds is, that they take hold of the work so 
deeply that they are very liable to break by the force requi- 
site to turn them round. Six and eight-sided, and square 
and half-round reamers, which have become slightly crooked 
in hardening, may be straightened by screwing a chipping 
hammer (flat face uppermost) between the jaws of a pair of 
vise ; the convex side of the reamer may then be laid upon 
the hammer face, while the concave side is slightly ham- 
mered with the sharp peen of a small hammer, at the same 
time pressing with the fingers upon each end of the reamer. 
If the reamers (previous to hammering) be slightly heated, 
they will straighten the easier, and be less liable to break. 

Small drills, gouge bits, center bits, countersinks, gim- 
lets, bradawls, or sprig bits, etc., may be expeditiously 
hardened by dipping their cutting parts into red-hot lead, 
and then cooling them in water. When it is intended to 
dip several 'of any of these kinds of articles at once into 
red-hot lead, it will be necessary to have a pair of tongs 
with long jaws for gripping the articles. One of the jaws 
of the tongs will require to be made hollow inside, and the 



Hardening and ' Temper ing Steel 133 

other jaw made flat; the hollow jaw is for convenience — 
for binding a piece of wood into it — so that if the articles 
should happen to be of an unequal thickness, the tongs may 
grip them all, as the most prominent parts of them will sink 
into the wood. When the wood becomes too much worn, 
it may be replaced by another piece. Any quantity of these 
articles may be heated as expeditiously as a single article, if 
there be sufficient lead. Gouge bits, gimlets, bradawls, or 
sprig bits, will require to be tempered after they are hard- 
ened. They may be tempered by placing them upon a piece 
of hot iron, and heating them until a blue color appears 
upon their surfaces, and then pushing them off the hot iron 
into a vessel containing cold oil; or, if the heat has not 
been too suddenly applied, they may be allowed to become 
cool in the air of their own accord. A large quantity may 
be tempered at once by placing them in a proper vessel with 
as much oil or tallow as will cover them, and then placing 
the whole over a small fire, and slowly heating the oil until it 
will take fire if a light be presented to it, but not so hot as 
to burn when the light is withdrawn. The articles may then 
be lifted out of the oil (that is, providing the vessel is fur- 
nished with a false bottom), or the whole may be tipped out 
of the vessel upon a thin sheet of iron which is slightly 
curved and placed in a slanting position, with a vessel 
placed at the bottom to catch the oil ; the articles may then 
be allowed to drain and become cool of their own accord ; 
they will then be the same temper as if their surfaces were 
blued upon hot iron. 

Center bits and countersinks for cutting wood require to 
be tempered to a purple color. The heat may be applied 
to these either by a piece of flat bar iron, or by an iron ring 



134 '^'^^^ Treatment of Steel 

heated to redness, or they may be placed in a proper vessel 
containing oil or tallow, and then placed over a small fire, 
and the whole slowly heated until the oil yields a thick black 
smoke, but not so hot as to take fire if a light be presented 
to it. The articles must then be taken out of the oil, and 
allowed to become cool ; they will then be the same temper as 
if their surfaces were changed to a purple color upon hot iron. 

Red-hot lead is an excellent thing in which to heat any 
long plate of steel that requires hardening only on one 
QdgQ, for it need not be heated in any other part but that 
which is required hard, and it will then keep straight in 
hardening ; at least, it will keep very much truer than if it 
were heated in the midst of the ignited fuel of the fire. 

If a long steel plate which requires to be hardened only 
on one edge be heated in a furnace, or in the midst of the 
ignited fuel of a hollow or open fire, and then the whole 
body of it immersed in the water, it will become very much 
twisted and warped, and will cause a deal of trouble to set 
it straight again, even though the steel be tempered previous 
to being hammered, especially to those who are unac- 
quainted with the way of hammering and setting steel plates 
in a hardened state. If the plate be heated throughout its 
body, and if only one edge of it (the edge which is required 
hard) be immersed in the water, or, in other words, if the 
plate be only partially immersed, the plate will become, in a 
great degree, concave on one edge and convex on the 'other. 
The edge of the plate which goes in the water becomes con- 
vex, and the edge which does not enter the water becomes 
concave. This is owing to that part of the plate which is 
below the surface of the water contracting and becoming 
shorter by the loss of heat, and compressing the red-hot 



Hardening and Tempering Steel 135 

part of the plate which is above the surface of the water 
into a denser state ; moreover, after that part of the plate 
which was below the surface of the water has become quite 
cool, it will be in a slight degree longer than what it was 
when in its soft state, consequently this has a tendency to 
push the red-hot part of the plate round, and thereby help- 
ing to cause the uppermost edge of the plate to become 
concave. 

After the whole body of the plate has become cool, the 
hardened part, as well as the soft part of the plate, will 
sometimes be shorter than what it was previous to harden- 
ing, even though the hardened part did expand longer in 
hardening. 'J'his is caused by the soft part of the plate 
contracting by the loss of heat after the hardened part has 
become cool, and thereby compressing the hardened part 
into a denser state. If red-hot lead is used as a source of 
heat, and the edge of the plate only (which is required 
hard) be put into the lead, it is obvious that the other part 
of the plate will remain cool ; consequently, when the plate 
is entirely immersed in water, the hot part of the plate will 
not act with sufficient force to alter the cool part, conse- 
quently the cool part of the plate tends to keep the hard- 
ened part true. It may be inquired, if the part which goes 
in the lead expands longer in hardening, and is not able to 
act with sufficient force to compress the cool part, will not 
the hardened part become twisted and buckled ? The an- 
swer to this is : it will not become twisted or buckled by the 
expansion (though it may become crooked in a slight de- 
gree by the unequal hammering, or the unequal density of 
the steel), because the heated part of the plate has been 
compressed by the cool part during the time it was expanded 



1^6 The Treatment of Steel 

by the heat, consequently the expansion will generally be 
about equal to the compression, and the plate will be about 
the same dimensions that it was previous to hardening. 

Should the hardened part of the plate happen to become 
in a slight degree longer than what it was previous to hard- 
ening, it is a proof that the expansion predominates over 
the compression ; if, on the contrary, it becomes shorter, it is a 
proof that the compression predominates over the expansion. 

When it is intended to heat articles in red-hot lead, they 
ought not to be plunged too quickly into the lead ; plunging 
cold steel too suddenly into red-hot lead has a tendency to 
cause it to become crooked, in a similar manner as red-hot 
steel becomes crooked when it is plunged too suddenly into 
cold water. 

All articles which are heated in red-hot lead should be 
slightly moved up and down in the lead during the time 
they are becoming heated, otherwise the heat will be apt to 
terminate in a strict line, and will probably cause them to 
crack when they are immersed in the water. 

A very good vessel in which to heat the lead when one 
edge of a long plate is required to be heated, is made by 
taking a piece of 3-inch angle iron, a few inches longer 
than the plate to be hardened, and slitting and turning, and 
welding each end of the angle iron so as to form a kind of 
trough. A long fire will be required for heating the angle 
iron and the lead. A fire of any length may be made 
by taking a piece of wrought-iron pipe, and boring some 
holes into it in the direction of its length. The holes will 
require to be about 5 g of an inch in diameter, and about 
3 inches apart ; one end of the pipe must then be in- 
serted into the aperture of the tuyere. A row of bricks 



Hardening and Tempering Steel 137 

must be placed on each side of the pipe, at a suitable dis- 
tance from it, so as to leave room for the fuel and the angle 
iron between the bricks. The pipe will require to be cov- 
ered over with loam or fire clay, in order to keep it from 
burning ; previous to covering the pipe over, each hole 
should be stopped with a piece of wood, so that the loam 
may not get into the pipe, or stop up the holes in the pipe ; 
after the covering up of the pipe is completed, the pieces of 
wood may then be pulled out of the holes, and the fire 
lighted. The fire will burn with more regularity if the first 
three or four holes (at the end of the pipe which enters the 
tuyere) be a little larger than the others, as the blast is al- 
ways strongest at the far end of the pipe. A loose plug will, 
of course, be required for the far end of the pipe to stop the 
blast ; and if, at any time, the pipe becomes stopped by the 
ashes falling through the holes of the pipe, the loose plug 
may be taken out, and the ashes blown out of the pipe ; the 
plug may then be put back into its place. If more durable 
things than the angle iron and pipe be required, a long fire 
tile may be chipped out to the proper shape, and made to 
answer the purpose, and a small special furnace constructed 
for heating it. A pot for melting a small quantity of lead 
may be made by welding a plug into one end of a piece of 
wrought-iron pipe ; but this is not very durable, as the high 
temperature of the lead will soon cause it to burn into holes, 
and allow the lead to run out into the fire. 

When a more durable thing than the wrought-iron pipe is 
required, and a larger quantity of lead requires heating, a 
crucible similar to those used in brass foundries will be suit- 
able. Crucibles containing a large quantity of lead cannot 
conveniently be heated in a common smith's fire; con- 



138 The Treatment of Steel 

sequently, a suitable furnace must be constructed for the 
purpose. When it is necessary to heat the lead in a crucible, 
it should be made red hot previous to putting the lead into 
it ; and, in heating the crucible, the same plan must be 
adopted as that which is generally adopted in brass foundries ; 
namely, putting the crucible in the fire with its mouth down- 
ward, in order that the heat may act upon the inside and 
outside of the crucible at the same time, and so cause a 
more uniform expansion of the crucible, and lessen the risk 
of its cracking. The crucible need not be reversed until it 
has become red hot ; then it will be ready to receive the 
lead. If the crucible be put in the fire bottom downward, 
the heat for a time would only act upon the outside; conse- 
quently, it would cause an unequal expansion, and increase 
the risk of its cracking. 

Another thing to be observed is that the surface of lead 
when melted in open vessels becomes quickly covered with 
a skin, or pellicle. This is occasioned by the action of the 
oxygen of the atmosphere, the activity of which soon causes 
the skin to increase in thickness, and wastes the lead so fast 
that it becomes an object of importance to those who use 
much lead to check its formation, or convert it when formed 
into the metallic state again. Charcoal, or fatty substances, 
assisted by sufiicient heat, convert this dross, or oxide, into 
metal again ; but if a covering of charcoal or cinders be kept 
on the surface of the melted lead, the oxide will not form. 
When it is allowed to form, it not only wastes the lead, but 
is a great obstruction in getting the articles in and out of 
the lead. 

In a former part of this work it has been recommended to 
allow steel, when heating for hardening (in order to assist the 



Hardening and Tempering Steel 139 

process), ample time to soak, and become uniformly heated to 
its innermost center. In this place (on the subject of heating 
steel in red-hot lead) it is stated that large fluted reamers 
may be immersed in the water, without fear of breaking 
them, immediately their cutting ribs or edges become uni- 
formly heated to the proper temperature suitable for harden- 
ing them, wdthout waiting for the central steel to become 
heated. As this will be probably noticed by some persons 
who may not perhaps give it sufficient thought to ascertain 
the true meaning of it, it will then appear to them that one 
part of the work is in contradiction to the other part ; con- 
sequently, I have thought it necessary in this place to give 
an explanation to it so as to prevent the reader misunder- 
standing it. In the first place it will be necessary to repeat 
that red-hot lead will heat steel much quicker than the ignited 
fuel of the fire ; consequently, when such an article as a 
large fluted reamer is dipped into the red-hot lead, the sur- 
face steel will become uniformly heated before the central 
steel has acquired sufficient heat to cause it to expand (at 
least from the short time the reamer is in the lead, the cen- 
tral steel can only become expanded in a very small degree); 
consequently, when the reamer is immersed in the water, 
the surface steel, in cooling, has not to compress the central 
steel, neither has the central steel to contract after the outer 
crust is fixed ; consequently, a large iiuted reamer may be 
immersed into the water (without risk of breaking it) imme- 
diately the cutting ribs arrive at the proper temperature suit- 
able for hardening them. If the surface steel of any article, 
when placed in a hollow or open fire, could be uniformly 
heated without heating or expanding the central steel, there 
would be no necessity for allowing the steel to soak or be- 



140 '/'//(? Treatment of Steel 

come uniformly heated to its innermost center ; but as the 
surface steel cannot, in a hollow or open fire, be uniformly 
heated without causing the central steel to become heated 
and expanded also, it becomes then quite necessary to heat 
the central steel to the same temperature as the surface 
steel, in order that the central steel may admit of being com- 
pressed by the surface steel when it is immersed in the 
water. When the central steel of any article becomes heated 
and expanded, and not sufficiently softened to admit of 
being compressed by the surface steel (when becoming cool), 
it will have a tendency to hold the surface steel in such a 
state of tension that it will sometimes cause it to crack in 
several places, and the surface steel will sometimes shell off 
in flakes; consequently, it must be seen that if the central 
steel is heated at all, it is requisite to heat it uniformly with 
the surface steel ; it will then lessen the risk of its breaking 
in hardening. For further information upon this subject, I 
must refer the reader to the chapter upon the expansion and 
contraction of steel. 

When it is required to harden large or small drifts in 
large or small quantities, they may be heated in a similar 
manner as screw taps, either by enclosing them in an iron 
box and surrounding them on all sides with carbon, and 
placing the whole in a furnace or hollow fire, or by placing 
them in the midst of the ignited fuel of a hollow fire. 
Whichever method be adopted, they will require to be uni- 
formly heated to a cherry-red heat. When they arrive at 
the proper heat, they will require to be immersed, separately, 
endways, perpendicularly, and slowly, in the water and en- 
tirely quenched. After the drifts have become quite cool, 
and been taken out of the water, they will require to be 



Hardening and Tempering Steel 141 

brightened and tempered ; they may be tempered by adopt- 
ing similar methods to those which are to be adopted for 
tempering screw taps. Drifts will require to be tempered to 
a brown color. 

When it is required to harden a quantity of large com- 
mon drills, and which have been allowed to become quite 
cool after having been forged, they may be placed, several 
at once, or as many as convenient, in the midst of the ig- 
nited fuel of a very small hollow fire, or they may be heated 
in an open fire, taking care to keep their points out of the 
hottest part of the fire at first, and gradually drawing their 
points toward the hotter part of the fire as the upper parts 
become heated. A considerable portion of the drill will 
require to be heated to a cherry-red heat. The blast, of 
course, must be sparingly used. When the drills arrive at 
the proper heat, they must be taken out of the fire sepa- 
rately. Those in advance of the others must be the first 
to be taken out ; a part of the heated portion of the drill 
must then be immersed in the water. It must not be 
forgotten that it is requisite to put the water in motion 
previous to dipping the point of the drill into the water, or 
otherwise, to give the drill a vertical, or other movement, 
immediately it arrives to the proper depth in the water. That 
part of the drill which is below the surface of the water must 
be allowed to remain in until it becomes quite cool, after 
which it must be taken out, and the cutting part brightened, 
which may be done by rubbing the surface with a piece of 
grindstone, or with an emery stick, or with a piece of emery 
cloth. The drill may then be laid upon the anvil, or any 
other suitable place, whilst another is draw^n out of the fire 
and treated in a similar manner. The heated portion of the 



T4'2 The Treatment of Steel 

drills which were not immersed in the water will then con- 
tinue to supply the heat to temper the cutting parts of the 
drills. After the second drill has been immersed, it may be 
placed alongside the first drill, and another drill withdrawn 
from the fire, and so on, until all that have been heated have 
been immersed. The hardener must, of course (during the 
time he is drawing the drills out of the fire and dipping them 
into the water), have his attention upon those he has placed 
upon the anvil, so that he may see when the cutting parts 
arrive at the proper temper ; as soon as a uniform dark straw 
color appears upon the cutting parts of the drills, they must 
be instantly cooled in the usual manner, otherwise the upper 
part of the drills may continue to supply heat, and the 
cutting parts will become too soft. Should it happen that 
the heat at the back part of any of the drills is insufficient 
to temper the cutting part, it will be advisable, in order to 
complete the tempering, to hold the drill for a few moments 
in a gas flame, if the gas is lighted ; or it may be placed 
upon a piece of hot iron, if there is a piece of hot iron ready 
at hand ; or a few hot ashes may be drawn out of the center 
of the fire, and the drill held over them. All drills which 
are intended to bore holes less than }^ of an inch (and when 
a quantity are required to be hardened) must not, like the 
larger kinds, be heated and partially immersed ; but their 
cutting parts only should be heated to a cherry-red heat, and 
the drills wholly immersed and entirely quenched. They 
may subsequently be tempered, by first brightening their 
cutting parts, and then placing them several at once upon a 
piece of bar iron heated to redness. Their cutting parts 
must be allowed to project some distance over the heated 
iron, otherwise the heat will be too suddenly applied. 



Hardening and Tempering Steel 143 

As soon as a dark straw color appears upon their cutting 
parts, they must be cooled in the usual manner. 

Miniature drills, such as those used by clock makers and 
others, cannot conveniently be heated in the midst of the 
ignited fuel of the fire ; though some of them may be heated 
in charcoal dust, heated to a red heat. These small drills 
are generally heated in a gas fiame, or in the flame of a 
candle ; they are hardened by plunging suddenly their heated 
points into a lump of tallow or into the grease of the candle. 
They are tempered, if found too hard, by taking a little of 
the tallow upon their points, and then placing them in the 
fiame at a short distance above the point, and holding them 
there until the tallow upon the point begins to smoke; the 
cutting part of the drill is then of the same temper as if it 
were brightened and tempered to a straw color. By any of 
the methods just explained, the cuttmg parts of the drills 
are tempered to a straw color, while the rest is not higher 
than blue, so that the liability of their breaking, when in 
use, is greatly diminished. 

It has previously been stated that chipping chisels will 
be the better, if the hammering (when forging them) 
be continued until the cutting part becomes nearly cool ; 
and, perhaps, it will not be amiss to state here that 
it is better to harden and temper them after being forged, 
and while the part above the cutting edge is in a 
red-hot state, than to allow them to become quite cool, 
and then to reheat them for hardening. The reason for 
this is, greater care is required to heat them properly 
after they have become quite cool ; consequently, there 
is greater risk of the effect of the hammering being taken 
off again. 



144 '^'^^^ Treatment of Steel 

When a large quantity of chipping chisels have been 
forged, and have been allowed to become quite cool, and 
which may require to be hardened and tempered, similar 
methods must then be adopted as those which are to be 
adopted for hardening and tempering the largest kinds of 
common drills, with the exception that the chisels will 
require to be tempered to a violet color, that is if they are 
required for chipping metals. If the chisels are required 
for chipping stone, they will require to be tempered to a 
purple color. The force required for chipping stone being 
less than for metals, it is obvious that the chisels are less 
liable to break ; consequently (in order to prevent them 
wearing away so fast), they may with safety be left in a slight 
degree harder. 

When it is required to harden those kinds of small chip- 
ping chisels which are used for chipping the delicate kinds 
of work, they must not, like the larger kinds, be heated and 
partly immersed, but their cutting part only should be heated 
to a cherry-red heat. They should then be wholly im- 
mersed, and entirely quenched. They may subsequently be 
tempered, by first brightening their cutting part, and then 
placing them, several at once, upon a piece of bar iron 
heated to redness. As soon as their cutting part becomes 
changed to a violet color, they must be instantly cooled in 
the usual manner. 

When a common turning tool is required extraordinarily 
hard, for cutting very hard cast-iron, it will be necessary, in 
the first place, to heat the tool to a red heat, and then give 
it a judicious hammering until it becomes nearly cool, after 
which it will be necessary to heat some lead to a bright red 
heat ; a small quantity of charcoal dust must be placed upon 



Hardening and Tempering Steel 145 

the surface of the heated lead to prevent oxidation. During 
the time the lead is becoming heated, the cutting part of the 
tool should be heated to a low red heat in an open fire. 
After the lead has become heated to a bright red heat, and 
the cutting part of the tool to a low red heat, the tool must 
be drawn out of the fire, and while it is at a red heat the 
scale must be removed with the file ; the cutting part of the 
tool must then, as soon after filing as possible, be put into 
the heated lead. It must be allowed to remain in the lead 
until it becomes heated to the same temperature as the lead 
— a bright red heat ; after which it must be taken out of the 
lead and instantly plunged into a bucket of pure cold water, 
and a rapid movement given to it, and entirely quenched ; 
after which, when taken out of the water and ground upon 
the grinding stone, it is ready for use. By this method the 
steel acquires a greater degree of hardness than will be 
readily imagined by those who have never tried it. 

When it is required to harden small spiral springs which 
are made of steel wire, or springs for locks, or any of the 
other kinds of slight springs, they will require to be uni- 
formly heated to a cherry-red heat, and then immersed in 
cold oil (not oil which has been long in use and become 
thick), and entirely quenched. Springs of a medium thick- 
ness will be the better for being cooled in water, the water 
being previously heated to about 60 degrees of heat, and 
the surface of which should be covered with a film of oil. 
The thickest kinds of springs will be the better for being cooled 
in pure water heated to about 70 degrees of heat. Springs 
require to have the greatest amount of elasticity given to 
them ; consequently, they will, after they are hardened, re- 
quire to be tempered. They may be tempered separately. 



146 llie Treatfnent of Steel 

by smearing them over with oil or tallow, and then holding 
them over a clear fire, or in a hollow fire, or in the inside of 
a piece of large iron pipe inserted in the midst of the ignited 
fuel of an open fire, and uniformly heating them until a 
white flame burns upon them, or, in other words, until the 
grease burns off with a blaze. If it is a spiral spring (or 
any other kind of spring which is not thicker at the ends 
than at the central part) which is being tempered, and 
which is shorter in its length than the length of the fire, it 
will be very apt to become heated at the extreme ends first ; 
consequently, as soon as the two ends arrive at the proper 
temperature (which is known by the grease taking fire), the 
spring must be immersed in oil ; it must not be entirely 
quenched, but must be taken out of the oil again immedi- 
ately, and then again exposed to heat. If the oil upon the 
ends takes fire again sooner than the oil upon the middle 
part of the spring, it must then be immersed again in oil, 
and then again exposed to heat, and so on until the oil burns 
uniformly upon all parts ; otherwise the spring cannot acquire 
a uniform temper. After the spring has become uniformly 
heated to the proper temperature, and the oil burns uniformly 
upon it, it must then be again immersed in oil, then taken 
out again immediately, and allowed to become cool in the 
air of its own accord. It will then be fit for use. All kinds 
of springs, whatever their shape, or whatever their size, may 
be tempered perfectly by this method. It must be borne in 
mind that there is but one certain temper which gives to 
steel its greatest amount of elasticity ; consequently, the 
stiffness or pliability of springs must be regulated by the 
substance and shape of the steel from which they are made. 
A very convenient way of tempering a large quantity of 



Ha7'den'mg and l^empering Steel 147 

small springs at once (they must, of course, be previously 
hardened), and of heating them uniformly, no matter how 
irregular their shape, provided the heat is not too suddenly 
applied, is to bind a quantity of them together with a piece 
of iron binding wire, and then to put them into a suitable 
vessel with as much oil or tallow as will cover them. Then 
place them over a small clear fire, and slowly heat the 
whole. Just as the oil begins to boil the springs must be 
lifted out, when a white flame will burn uniformly upon the 
whole of them ; they must then be immersed into cold oil — 
they need not be entirely quenched, but they may be taken 
out of the oil again immediately, and allowed to become 
cool in the air of their own accord, and when cool, they will 
be like those which have been blazed off separately over the 
fire, and fit for use. A separate spring may be attached to 
a separate piece of "wire, which may be lifted out of the oil, 
occasionally, to ascertain w^hen the whole is at a proper 
heat, which is known by the white color of the flame upon 
the spring. 

Large springs may be tempered by this method, but the 
time saved with large springs will not be suflicient to compen- 
sate for the waste of oil ; consequently, it will be more econom- 
ical to temper the largest springs by blazing over the fire. 

It will be well for those who are not accustomed to the 
operation, before attempting to boil a large quantity of 
springs, to boil a single one in a small quantity of oil, and 
so make themselves acquainted with the proper temperature 
of the oil, and the proper temper of the spring. 

I will now bring this chapter to a conclusion, not because 
I have no more to say, but because I do not think it neces- 
sary to say more ; but I may add that the hardness of 



148 The Treatment of Steel 

cutting tools and the angles forming their edges must be 
varied according to the strength and hardness of the 
material to be worked. The harder materials require tools 
with more obtuse-angled edges, and no cutting tool will act 
upon a substance harder than itself. 

The number of turns w^hich the mandrel of the lathe 
ought to make in a given time must also be varied according 
to the strength and hardness of the material to be worked. 
The velocity of rotation for wood can scarcely be too swift ; 
it must be rather slow for lead, brass, copper, gun metal and 
bell metal ; still slower for ordinary cast-iron, forged iron and 
steel, and slowest of all for tempered steel and chilled cast- 
iron, or, in other words, for cast-iron which has been cast in 
iron molds, or other good conductors of heat. 

The reason for these limits is that a certain amount of 
time, varying with the material, is requisite for the act of 
cutting to take place, and that the tools, if much heated, w ill 
instantly become soft and cease to cut. 



Selt-hardening Steel 



The alloy steels derive their peculiar properties from the 
addition of certain elements or compounds of the metal 
group, as tungsten (wolfram), chromium, molybdenum, nickel 
and manganese, the two latter, however, when used as alloys, 
imparting conditions which have thus far excluded nickel 
and manganese steel from the self-hardening tool steel class. 

Self-hardening steel finds its most valuable uses in heavy 
rouo;hino- work where time saved is the main factor to be con- 
sidered, its peculiar properties enabling it to hold a cutting 
edge at speeds which would draw the temper all out of carbon 
steel. For this reason it has come into general use in shops 
where machine tools are pushed to their utmost capacity. 

Owing to the difficulty of annealing and machining self- 
hardening steel its use was at first confined to simple forms, 
such as lathe and planer tools which could be forged to shape 
and ground on an emery wheel or grindstone, and to nail dies 
and knives and similar purposes ; afterwards it was success- 
fully applied to boring bar cutters, milling cutter blades, etc. 

A process of annealing has since been perfected which 
admits of this steel being readily machined to any shape. 
All kinds of cutters are now made from it, these when 
finished being merely reheated and laid down to cool ; a 
simple process which eliminates the danger of cracking or 
warping to which all complicated shapes are exposed when 
hardened in the bath. 

The heat treatment applicable to self-hardening steel 
varies according to the variety or to the particular element 
which is dominant in it. 



T 50 The Treatryicnt of Steel 

Several modes of "special treatment" have been dis- 
covered and applied to self-hardening steel tools, and have 
greatly added to their endurance, but as knowledge of these 
has not yet been given to the public, allusion in this article 
will be made only to general treatment. 

To break self hardening steel into lengths for tools, the 
piece should be carefully heated to a uniform, bright red and 
cut with a sharp chisel nearly or quite through, or nicked all 
around while hot and broken ofT cold. 

The heating for forging should be done in a pure fire : 
sound charcoal or coke in a bed of generous proportions if 
the heating is to be done on the forge, and coke or gas if in a 
furnace, will be found to be advantageous. Fine steel should 
never be heated in green fires. If coal must be used, the 
impurities should be burned out before putting in the steel. 

Where the heating is done in the open fire, that portion 
of the piece which is to form the cutting end, — if an oblong 
shape, — should, when first put in, extend a few inches beyond 
the heart of the fire in order that the heat may be taken up 
by the body of the piece and be carried by conduction slowly 
to the projecting end, which should be gradually drawn into 
the fire. 

The heating should be slow and the blast as gentle as 
possible. The piece should be turned from time to time 
until the portion to be forged, and the adjacent parts, are 
brought up to a full, bright red heat ; then it should be 
forged to the required shape. 

The force of the blows and the weight of the hammer 
employed in forging should be in accordance with the size 
of the piece operated upon. Self-hardening steel is more 
dense, less plastic and less malleable than carbon steel, and 



Self- hardening Steel i 5 1 

cannot be shaped as readily. A large section requires a 
heavy hammer that will act upon the entire mass, as too 
light a hammer will draw away the surface from the center 
and produce a rupture. On the other hand a very heavy 
hammer on a small piece will crush or break the steel. 

Before the steel loses its malleability, as it will to a great 
extent upon reaching a dark red, it should be reheated, and 
the heating should be repeated as often as may be necessary 
until the forging is completed. 

It is important that during the entire work the heat of 
the piece should be maintained as nearly as possible at one 
uniform temperature ; especial care should be taken to avoid 
forging below a dark red ; if forged too cold the steel will 
be injured. 

After the forging work is completed the piece should be 
replaced in the fire with the blast off, and brought to a 
uniform bright red color. As soon as this condition is 
attained fully, it should be laid down to cool in a dry place 
free from draughts. Water should not touch it at any stage. 
When cold, if the shape admits of so doing, it can be ground 
to an edge. 

Some kinds of self-hardening steel are improved in their 
cutting qualities by being cooled in an air blast ; others work 
better if cooled more slowly, and some require to be cooled 
in such a way as to partially anneal them. 

If the last reheating has been done properly, the piece 
will be not only hardened but tempered, since the uniformity 
of the heat takes out the strains put in by forging, and the 
gradual cooling reduces the brittleness. The last" heat is in 
reality an equalizing heat producing the same effect as in 
the tempering fire. 



152 The Treatment of Steel 

If, however, the piece htill appears to be brittle, it may 
be "tempered" by being again heated carefully and uni- 
formly to a bright red, as before, and then cooled slowly in 
the ashes on the forge until it reaches a dull red, when the 
cooling may be completed in the air or in an air blast. 

One mode of full annealing is accomplished by heating 
in a furnace or muffle to a low red, maintaining the tem- 
perature uniformly for a period as long in some instances 
as forty-eight hours, and then letting the steel cool slowly, 
covered up from the air. 

The operation is expensive and tedious, however, and 
had best be relegated to the steel maker. 

There are brands of steel on the market which partake 
of the nature of self-hardening steel, yet can be hardened 
like carbon steel if the heating is carefully done. 

Instructions for working such steel are generally given 
on the labels, but in the absence of specific directions this 
semi-self-hardening steel should be forged in the manner 
described for self-hardening steel, but at a slightly lower 
heat, and the final equalizing heat should not exceed a 
low red, which should be perfectly even. 

At this temperature the piece may be quenched in heavy 
thick oil and need not be drawn. Some kinds may even be 
plunged into a water bath. 

If the heating is carefully done the tool may be used at 
full hardness. 







Overheated steel tells its own story. 

A high heat opens the grain of steel and prevents 
refining. 

Cast-steel properly hardened is invariably refined thereby. 

'I'he temper of steel is regulated by percentage of carbon. 

The iron used in making steel determines its quality. 

Consumers of steel should be guided by makers' advices. 

Sulphur is an enemy to steel. 

Good fuel is essential to best results in working steel. 

Charcoal, from sound wood, is the king of fuels. 

Avoid exposing hot steel to draughts of air. 

Pure water is a good hardening medium. 

Cherry red is a safe heat for steel. 

Nick cold steel with sharp chisels. 

A good softening heat, for forging, can be safely used if 
proper precautions are observed. 



I 54 The Treatynent of Steel 

The lead screws of lathes are often responsible for inac- 
curacies in the threads of taps. 

Large pieces may often be protected in heating by being 
covered with a coating of dry clay. 

No annealing is better than over-annealing. 

Be sparing of the blast. 

Time and care are necessary in the treatment of steel. 

Burnt steel is disintegrated steel. 

Properly constructed furnaces will pay for themselves in 
the value of tools which will be saved by their use. 

" Soaking," or long continued heats, even if low, are 
injurious to steel. 

It requires a high order of talent to treat high-grade steel 
successfully. 

In heating for hardening, great care should be taken 
with irregular shapes that no part of the piece be too hot. 

Steel which has been annealed at a high heat will not 
harden on the surface. 

A low red heat will anneal steel thoroughly. 

Do not try to harden steel that has been annealed, before 
taking off the surface. 

He is a good steel worker who never spoilt a piece of steel. 

Do not be deceived by nostrums for restoring burnt steel. 

The peculiarities and proper treatment of steel are studies 
for a lifetime. 



sparks I 5 5 

Benjamin Huntsman invented the cast-steel process 
in 1770. 

Crucible cast-steel is recognized the world over as the 
best sieel. 

I.ow-priced steel may be very dear steel. 

Steel is mercurial and delicately responsive to heat; its 
records appear in its own structure. 

The last age : the age of steel. 

Dirty, slack fires put dirty sulphurous oxides on steel. 

The hardening heat varies with each temper of steel, 
and the only safe course is to harden at the lowest heat that, 
on trial, is found to give the required hardness. 

Hardening cracks are more often the result of uneven 
heating than of defect in steel. 

Tool hardeners do not always realize what a slight addi- 
tion of heat it takes to raise the grain beyond the refining 
point and create a weak condition. 

Heat steel slowly, but do not run to the other extreme 
by taking too much time in heating. 

Uneven heat, too high heat, and heat too long continued, 
are responsible for many errors. 

Always harden on an ascending heat; never on a 
descending heat. 

Large baths are always safer than small ones. 

Large centers in taps and reamers are a cause of cracks; 
close them up. 



^6 The iyeat?nent of Steel 



Clean coke is by many considered preferable to char- 
1 for heating 
a more even fire. 



coal for heating steel to forge, or harden, because it makes 



There is no other way to prevent slender taps, reamers 
and twist drills from springing, than to heat them carefully. 
Even then some will come out curved, but they can be 
straightened while the temper is running. 

Boring holes too near the outside of some articles will 
oftentimes cause the article to crack at the hole. 

Sharp internal angles are unfavorable to the strength of 
articles ; and any description of sharp angles is unfavorable 
in the hardening process. 

Cutters used for cutting soft substances, such as brass 
and copper, require to have their teeth very sharp, and to be 
made very hard. The teeth also require to be cut much 
coarser than for iron or steel. 

Generally speaking, in dipping articles for hardening which 
are of unequal thickness, the thick part should enter the 
bath first. 

To insure even hardening, take off plenty of the surface, 
heat evenly and quench in a large bath. 

When a bright surface is hardened, there is more danger 
of cracking than where the piece is protected by its coating 
of oxide of iron or scale. 

Avoid heating a piece to a strict line for hardening ; 
likewise avoid dipping to a strict line. 



Index 



Advertisement 



i6 



Pages 
). 164 



Alloy steels 149 

Analysis of twelve ingots . 36 
Angles of cutting tool edges 148 

sharp .... 58, 105, 106 
Animal charcoal 77,91 106 107 
Annealing 7-9, 49, 50 

and hammering, necessity of c;4 
Applying heat, methods of . 64 

for tempering circular cut- 
ters 9: 

Art of hardening .... 

of tempering .'.... 



Awls, brad 



I-,2, 



'93 

66 
133 



liath, temperature of 74-76,90, 
water . ." 63,81-85,87, 
... 74- 



8i- 



99> 
132, 
132, 



soft water best 

removing from too soon 

depth of water in . . 

moving about in . . . 
Bean or flour meal . . . 
Bits, gouge .... 

sprig 

Blades, thin ..... 

Black lead 

Boiling temperature, cooling 
from, hardens ... 42 

in water to relieve strains 
Box heating, 64, 77, 86, 88, 89, 91 

101,106,107,1 14,115,121,128, 
Boxes for heating, how to 

make 114, 

Bradawls 132, 

Brass cutting tools .... 
Breakage by taking out of 
bath too soon . . . Si 

Brightening 

Bright articles, heated in con 
tact with carbon . 77, 

liability of breakage 
Brinish liquids .... 

Burned 

Burnt structure, illustration 
opposite page . . 



7^, 



93 

88 

76 

-83 
96 
101 
100 
'33 
133 
122 
129 

.43 

93 

>95 

140 

115 
133 

58 

-S3 
91 

91 
80 
76 
50 



Pages 

Burst II 

Bushes 90 

Candle, heating in flame of 65, 77 

Carbon, 5 (preface), 25,26,31,32 

effects of . . 8 (foot note) 

27, 28, 35, 36 (table), 37, 39 

40, 44 (table), 45-49' 53. 77 

range of 31 

Case-hardening (see prussiate 

of potash). 
Centers, deep . . . . 106 

lathe 128 

Center bits .... 132, 133 
Certainty that articles are hard 68 
Changes in volume, due to 

temperature (table) . . 37 

due to annealing ... 41 

Charcoal, bad conductor of heat 68 

animal and wood 77, 91, 106 

Chasers 1 17, 118 

Cheap steel is dear ... 28 
Chemical composition . 30, 31 

properties 61 

Chipping chisels . 85, 143, 144 
Chisels and drills, ends drop- 
ping off 85, 86 

colors for 144 

Choosing steel .... 54, 55 
Circular cutters . . . 55-57, 62 
88-90, 98, 99 
large, tempering unneces- 
sary 93,99 

tempering color ... 92, q^ 

Circular dies 60 

Circular saws . . . 121-125 
Cold, intense, has unfavora- 
ble effect . . • • 63 
Cold hammering, effects of 41, 42 

Collars 62, 90, 100 

Collar or eccentric ring . . 100 
Collars or rings with unequal 

edges 95-97 

thick edge must enter 
water first 96 



I 'ages 

Colors, tempering 66, 67, 70-72, 93 

94, 109, 124, 125 

132, 133' 142-144 
for center bits . . . 133 

for chipping chisels, small 144 

for chisels 144 

for countersinks . . . . 133 
for cutters .... 91-93 

for drifts 141 

for drills .... 142, 143 
for engraved dies ... 94 
for miniature drills . . . 143 

for reamers 132 

for saws . . . . 124, 125 
for circular saws .... 1 23 
for hand wood saws . . 125 
for metal saws .... 128 
for screw dies . . . . 116 
for springs . . . . 72 

for taps . . . 1 09- 1 II, 113 
for master taps . . . . 113 

for chasers 117 

for screw plates . . . . 119 
for clock springs ... 72 
for fluted reamers . . . 132 
for six and eight-sided 

reamers 132 

for square and triangular 

reamers 132 

for gouge bits . . . . 133 

for bradawls 133 

for sprig bits 133 

Contraction and expansion 55, 61 
62,74,75,134,135 

Cooling 92 

in air 70, 151 

in air blast 151 

Countersinks . . . '32, 133 

Cracking 45 

Cracks, water 85, 87, 88, 104, 105 

Crooked drifts 86 

taps 107, 108 

Crooked reamers . . 130-132 
how to prevent . . 130-132 
how to straighten 130-132 

article, when heated in 

lead 136 

Crucible, for heating lead 137,138 



Pages 

Cutters 88-93 

feather-edge .... 98-100 
small, tempering colors for 91-93 

valuable hint 57 

Cutting tool edges, angles of 148 
Cylindrical lump .... 62 

Dangers of heating in oil . 73 

Dear steel 28 

Deep centers 106 

Designing tools .... 53 

Dies 90 

engraved 94 

tempering color for . . 94 

hardening a second time . 95 

Dies, screw .... 114-116 

tempering . . . . 115, 116 

Dipping, circular cutters . 88-90 

partial 84, 85, 87 

tool for 88-90 

Drawing temper . . . 91-94 

Drifts 86, 87, 140 

crooked 86, 87 

Drills S6, 141-143 

small 132, 143 

colors for . . . . 142, 143 
Drills and chisels, ends drop- 
ping off 86 

Precentric ring or collar . . 100 
Eccentric steel collar ... 62 
Edges of cutting tools, angles 

of 148 

Effects of carbon 8 (foot-note) 

27, 28, 35, 36 (table), 37,39,40 

44 (table), 45-49, 53, 77 

Effects of cold hammering . 41 

42 (table) 

Effects of heat upon steel . 20 

Effects of temperature and 

changes of temperature 30 
Effects of work . . • 30, 3 3, 39 

Engraved dies 94 

hardening a second time . 95 

Expansion and contraction 55,61 

62,74,75, 134, 135 

Feather-edge circular cutters 98, 99 
Fires, for short heats . . . 103 



I'aj;es 

Fire, hollow 64 

open 64 

Flour or bean meal . . 99, 100 
Fluted reamers . . 1 28- 131, 139 

Flux, welding 12 

Furnaces, description, uses, 

heat, treatment . . 15-19 

grate-bars in 16 

fuel for 17 

cost of 19 

heating in 64 

Further reduction in temper 70 

Gas flame, heating in 65, 77, 143 
Gas stove, heating on . . 69 

Gauges 29, 90, 91 

Gimlets 132, 1 33 

Gouge bits .... 132,133 
Grain of steel, illustrations, 

opposite pages . . . 6, 20 

natural bar 6 

refined 6 

burnt 6 

Grain and strength, how to 

test 19 

Grate bars in furnaces, illus- 
tration 16, 18 

Half-round reamers . . 130, 132 
Hammer refining .... ^3 
Hardening, from boilmg tern 



perature . 
repeated 
throughout 
at strict line 
partial . . 
superficial 



• • 42, 43. 46 
■ • 36.44,45 
.... 83 
. . . 83-S8 
83-88, 102-104 
I, 22 (foot note) 
140 



23, 139 

engraved dies a secondtime 95 

I lardening art, knowledge of 52 
Hardening and tempering . 51 

I I ardened steel occupies more 

space 88 

Hardness of cutting tools . 148 
Heat, effects of, illustrations 

opposite 20 

high 13 

charcoal, a bad conductor of 68 



r'ages 

irregular 13 

lowest best 13 

methods of applying . . 64 

soaking 8, 12, 139 

variations in 13 

Heating in oil .... 71-73 

dangers of 73 

Heating 10 

for forging 10-14 

for hardening . . . . 10-14 

for tempering .... 10-14 

Heating in boxes 64, 68, 77, S6 

88, 90, 10 r, 106, 107 

in furnaces 64 

in lead 64, 83. 104 

in gas flame . . . 65, yj, 143 
in candle flame ... 65, 77 
in jaws of tongs ... 65, 77 
in nicked iron bar ... 65 
in iron pipe 22 (foot note), 65 
114, 115, 136, 137 
in sheet-iron pan ... 87 
on piece of iron . . . . 133 
between two heated bars . 77 
High heat, in forging ... 15 

Hobs 59, 60, 113 

Holes near edges . . . . 10 1 

filling with loam . . . 102 

Hollow fire . . . .64,65,75 

How to test grain and strength 19 

Intense cold has unfavorable 

effect 63 

Immersion, mode of . . . 74 

Iron ring 133 

Irregular heat 13 

Keyway with sharp angles . 106 
Keyvvays in cutters ... 58 
Knowledge of the hardening 
art 5'. 52 

Lampblack 129 

Lathe centers 128 

Lathe mandrel, speed of . . 148 
Lathe tools , . . . 141, 145 
Lead, how to cool it down . 129 
Lead heating, 64, 83, 104, 129-132 
134-139 



vessel for . 

crucible for 

pipe for 

oxidation, how 
Linseed oil 
Loam, use of 

prevents hardening 



Pages 

• • 136, 137 

• • ^31^ 138 

• • 136, 137 

to prevent 138 
. 129 



Long plate hardened on one 



edge 
Lowest heat best 
Lumps, spherical 
square 



Mandrel holes, size of 
Mandrel, lathe, speed of 
Master taps or hobs . 

Mercury 

Mode of immersion 
Moving about in bath 



104- 

104- 



134- 



106 
■106 

136 
64 
62 
62 



56 
148 

113 
76 

74 

lOI 



Natural bar, structure, illus- 
trations, opposite pages 6, 20 

Oil film . . . . . . . . 122 

tempering 70-73» ^ZZ^ i -4 5-147 
temperatures .... 71-73 

On gauges 29 

On temper of steel .... 25 

Open fire 64 

and numerous references 

Partial hardening . 87, 102-106 

dipping 83-88 

Pipe, heating in 22 (foot note) 

114, 115, 136, 137 

Plug and ring guages . . 97, 98 

Polishing 91 

Preface to third edition . . 5 
Products of Crucible Steel 

Company of America 163, 164 

Prussiate of potash, 78, 79, 91, 95 

99-101, 105, 106, 108, 114, 119 



Quality versus temper 



28 



Reamers, fluted 58, 128-132, 139 

half round 130,132 

crooked 130-132 



Pages 
crooked, how to prevent 130-132 
crooked, how to straighten 

130-132 
large or deep centers in . 58 

colors for 132 

six and eight-sided . . . 132 

square 132 

triangular . . . . . . 132 

soft center in . 22 (foot note) 

139, 140 

Reducing substance and bulk 57 

Refining by hardening 21, 23, 34 

Refined, hardened, structure, 

illustrations, opposite 

pages 6, 20 

Repeated hardening . 36, 44, 45 
Restoring from overheating 

23' 24, 35' 49. 50. 64 

Rings 90, 91 

shrinking on . . . . 60, 61 

Ring guages 90, 91 

Rings or collars with un- 
equal edges . . . 95-97 
thick edge must enter bath 

first 96 

Round steel ... 59, 100, 10 1 
immerse endways and per- 
pendicularly .... lOI 

Sand bath 119 

Saws 78 

circular 1 21-125 

color for 124, 125 

blades 125-128 

buckhng 121, i 24, 126, 127 

Scale or skin 79? 81 

thick, unequal .... 8 [ 
Scale, ruining tools cutting it 1 20 
Scaling, prevention of . . 91 
Screw dies . . . . 114-116 

color for 116 

immerse screw end last . 114 

tempering 115, 116 

Screw plates 119,120 

Screw taps . . 5S-60, 106-109 

large or deep centers in . 58 

Self hardening steel . . . 149 

properties 149 



uses .... 
annealing . . 
heat treatment 
special " treatment 



Pages 

• 149 
149, 152 
149-152 

• 150 



to break into lengths . . 150 

forging 150, I 51 

heat treatment for forg- 
ing I 5O' ' 5 ' 

reheating 151, 152 

maintaining temperature . 151 
cooling in air or air blast . 151 

strains 151 

tempering or equalizing 

heat 151, 152 

brittleness 152 

semi-self -hardening steel . 1 52 
quenching semi-self-hard- 
ening steel 152 

Sharp angles ... 58, 105, 106 
Shrinking on rings . . . 60,61 
Six and eight-sided reamers 132 

Small baths 13 

Soap in water 76 

soft 129 

Soaking . . . . 8, 12, 88, 139 
Soft center in reamers . 139, 140 

Softening ends 104 

■' Sparks," sundry sugges- 
tions 153-156 

Specific gravities . . . 35-45 
Spherical lumps .... 62 

Sprig bits 132, 133 

Springs, spiral, hardening and 

tempering 72,73,127,145-147 

Spring temper 127 

Square cast-steel .... 102 
less liable to break than 

spherical 62 

reamers 132 

Steam in hardening bath . 93 
Steel, can it be worked safely? 48 

is it reliable ? 48 

high steel or low ? . . . 48 
how it is to be worked ? . 48 
is it safe to take advan- 
tage of strength ? . . 48 
is it necessary to anneal 

finished work ? . . . 48 



Pages 
structure and physical pro- 
perties 30,31 

is mercurial 49 

restoring . . 23, 24,35, 49> 5^ 
Stoutest part enter bath first 98 
bad effect of in some in- 
stances 100 

Strict line in lead heating, 134-136 
Structure and physical prop- 
erties ... 30, 31 et. seq. 
Sundry suggestions . . 153-156 
Superficial hardening . 139, 140 



Tallow 



122, 125, I 



hot, temperatures of 

danger in heating 

tempering in ... 71- 

Tank, arrangement for dip- 
ping taps .... 107, I 

Taps, screw .... 58-60, 
hardening .... 106-1 
immerse, screw end first . i 

crooked 107, i 

tempering .... IC9-1 
color for 109- 1 



master, or hob 
Temper versus quality 
Temper of steel , . 
Tempering, art of 

necessity of . . . 

certainty that articles are 
hard 

upon a bar of hot iron 

in a hot iron ring . . 

in melted lead . . . 

in mouth of furnace . 

in bath of fusible metal 

in an oven .... 

on a gas stove . 

in hot sand .... 

may be immersed . . 

may be cooled in air . 

from back of tool . . 

further reduction in tem 



113' ' 



per 

a large number together 
in hot oil or tallow . . 
in oil, danger of . . 



08 

14 
1 1 

14 

28 

25 

66 

63,64 

68 
69 
69 
69 
69 
69 
69 

69 
69 

70 

70 
70,87 

70 

71 

71-73 

73 



Pages 

dies 94, 115, 1 16 

cutters 9^~93 

in some instances not 

necessary 79, 80, 93, 97, 98 
Tempering colors 66, 67, 70-72, 93 

94,109-111,113,115-119,123- 

125, 127, 132-134, 141-144 
for engraved dies ... 94 

for reamers 132 

for drills . . . . 142, 143 
for cutters .... 91-93 
for miniature drills . . . 143 

for chisels 144 

for chipping chisels (small ) 1 44 
for taps . . . 1 09-1 1 1, 113 
for master taps . . . . 113 
for center bits .... 133 
for countersinks . . . 133 

for drifts 141 

for screw dies . . . . 116 

for springs 72 

for saws . . . . 124, 125 
for circular saws . . . 123 
for hand wood saws . . 125 
for metal saws . . . . 128 

for chasers 117 

for screw plates . . , 119 
for clock springs ... 72 
for fluted reamers . . . 132 
for six and eight-sided 

reamers 132 

for square and triangular 

reamers 132 

for gouge bits .... 133 

for bradawls 133 

for sprig bits . . • . 133 



Pages 
Tempering heat, not too 

sudden 67 

methods of applying . . 67 
Temperatures of hot oil and 

tallow 71-73 

Temperatures of water baths 

74,75 
Temperature changes, effects 

of 22, 23 

Thin blades 122 

Triangular reamers . . . 132 
Turning tools . 79, 80, 144, 145 

Unequal thickness and bulk 

55-5« 

Variations of heat ... 13 
Vertical movement . . 85, 86 
Volume, changes in by hard- 
ening (specific gravities) 

35-45 

Water becomes softer . 75, 76 
Water cracks .... 83-90 
Water not essential ... 63 
Welded steel, hardening . 84 

Welding flux 12 

What is steel ? . 5 (preface), 30 
et. seq. 
Why does steel harden ? (W. 

Metcalf, C. E.) . . . 30 

various theories . . 45-48 

practical considerations 48-50 

the correct answer ... 50 

Woodworking tools ... 84 

Work, effects of . . 30, 33, 39 



Crucible Steel Company of 
America 



Owning or Controlling Ore Properties, Blast Furnaces, Iron 

Fineries, Crucible Furnaces, Open-hearth Furnaces, 

Forges, Rolling Mills, Wire Mills and 

Sheet and Bar Copper Mills 



Producers of Steel by the Crucible and Open -hearth 

Processes in Bars, Rods, Sheets, Plates, Wire, 

Forgings and Rolled Shapes 



Principal Offices 
Pittsburgh, Pennsylvania, United States of America 

Eastern and Export Offices 

New York, N. Y. 

Depots throughout the United States and Canada 
Foreign Offices 

Hamburg, London, Melbourne 
Johannesburg 



The Products Include 



Fine Tool and Die Steel 

Self-hardening Tool Steel 

Axe and Hatchet Steel 

Cutlery Steel 

Surgical and Fine Knife Steel 

Composite Die Steel 

Oil Well and Artesian Bit Steel 

Mining Drill Steel 

Annealed Die Blocks and Cutter 

Blanks 
Tool Steel Forgings 
Circular and Long Saw Plates 
Boiler and Fire Box Plates 
Hot-rolled and Cold-rolled Band 

Saw Steel 
Hot and Cold-rolled Sheet, Band 

and Strip Steel 
Polished, High-grade Drill Rods 

and Wire 
Needle Wire 
Resistance Wire Rods 
Music Wire Rods 
Nickel Steel Rods 
Wire of every grade, shape and size, 

bright, annealed and tempered 

Etc. 



Crucible Steel Rods 

Clock and Watch Spring Steel 

Pen Steel 

Magnet Steel 

Heavy Gun Forgings and Pro- 
jectiles 

Gun Barrel Steel 

Spring Steel 

Machinery Steel 

Merchant Bar Steel 

Machinery Steel Forgings 

Cold-drawn Screw Steel 

Cold-drawn Shafting 

File Steel 

Pike and Cant Hook Steel 

Hammer and Sledge Steel 

Welding Steel 

Soft Center and Soft Back Plow 
Steel 

Agricultural Steel of all descrip- 
tions 

Sleigh Shoe and Toe-calk Steel 

Wedge Steel 

Laminated Safe Steel 

Skate Steel 
Etc. 



Rolled Shapes in Great Variety 



Steel of Every Description 



